I could definitely see this as an epic level 4e adventure. The only issue is that it works best in a world where there is a Heaven/Hell dichotomy. While it could work in a more generic world it may lose some of the impact.
The adventure begins with the PCs being asked to look into the local druid's grove, the Stone Circle. It is apparently the Grand Druid's personal grove and had been dealing with a lycanthopy outbreak in the area. Witnesses saw a large force of werebeasts heading towards the grove. Normally they would have expected the Grand Druid to send them running but things have gone worryingly quiet.
When the PCs arrive there are werebeasts of various types everywhere and lots of dead druids. The lycanthropes are wielding powerful divine magic items for some reason - it was apparently what gave them the edge for victory. Inside the Grand Druid's own abode is a force of werewolves trying to break down a warded door. Behind the door is a very frightened girl named Lilly, probably about six years old. She can open the door from the inside if the PCs can convince her. She's the only survivor of the attack.
Interlude 1 - Lilly
Lilly has a fanciful imagination. She says the nice men have been taking care of her for most of her life, but she has some memories of her mother and father. Her mother is a beautiful princess and is the one that left her with the nice men before being taken away by horrible monsters. Her father is also beautiful, has long blonde hair, blue eyes and fluffy white wings. Some bad men hurt him and made him go away. She has a note from her mother that says where to find her if she ever needs to - at Stonecrag Keep deep in the mountains.
High level characters will have all sorts of ways of getting information. However some of their more powerful effects will give odd results. The following are generalized responses if some sort of Commune ritual is cast:
L/G & L/N - The child must be destroyed.
N/G - Follow the good in your heart. We will say no more.
C/G - Reunite this poor child's family. Damn the hard asses.
N - Do as you wish. We are not interfering.
C/N - You've got who? Ha ha ha ha! This'll be good.
L/E & N/E - Interesting, want to make a trade?
C/E - ... we could care less.
Using various lore skills can fill in details about the Stone Circle - most importantly that it is considered neutral ground between the powers of Good and Evil. Lore about Stonecrag Keep reveals that it was once the seat of a powerful mountain kingdom but about four years ago its leaders made an ill-advised deal with some demons and the whole place was overrun. Now a marilith named Mairael rules in the king's place with her retinue of demons.
Before the PCs make a decisions they are approached by a man who calls himself Galriel. Lilly will immediately hide behind one of the PCs and whimper, "That's the man who hurt my daddy..." Galriel will demand that the PCs hand the girl over to him. He will quickly reveal that he is an angel and that the child is an abomination unto Heaven and must be destroyed. He'll refuse to go into any more detail. Hopefully the PCs will refuse. He'll give them one day to reconsider since they have been such forces for good in the world. This should also make it clear that if they want her kept safe then Lilly can't be left alone with anyone since she would be snatched up and killed by angels.
Part 2 - Stonecrag Keep
Stonecrag Keep is set into the side of a mountain with an aerial landing platform out front along with a long, winding trail up the mountain. The keep itself is fairly straightforward and inhabited with all sorts of demonic baddies. The trick is Lilly and how the PCs deal with having a six year old following them around inside a demon infested fortress. Lilly has innate energy resistance so that she'll survive almost all energy-based area attacks but if the PCs don't protect her from direct physical contact with something nasty... it's up to you if you can let her die.
The final chamber is the throne room full of demons and Mairael sitting on the throne with a succubus on either side of her. As soon as they enter the room Lilly will scream "Mommy!" and dash across the floor towards one of the succubi. Combat will begin with this - her mother will fight the demons to defend Lilly.
Interlude 2 - Mother and Daughter
Lilly's mother is a succubus named Luneelle, her father an angel named Elniel. Luneelle decided she would attempt the ultimate coup to gain some power and seduce an angel. She targeted Elniel, he responded... but she wasn't ready for the only type of love a being of pure goodness could give - true love. She found herself falling in love with him in return and against all odds became pregnant with his child. They tried to hide their affair and managed to keep it secret for three years, until Lilly was two. That was when the angels came. Elniel sacrificed himself so that Luneelle could flee to neutral ground where she could hide Lilly.
Elniel was slain and his immortal soul condemned to the city of Dis in Hell so that he couldn't return in angelic form. Luneelle took up with Mairael so that she could be relatively close to Lilly. Lilly was raised by the Grand Druid for the next four years. Now that the Grand Druid is dead she isn't sure where to go. She can shield them for a little while but only Elniel would know where they could be hidden from Heaven.
Part 3 - To Free an Angel
The third part is fairly straightforward - a raid on the prisons in the city of Dis in Hell to free an imprisoned angel. Okay, not that straightforward. Luneelle can get them there and get them out once they've got Elniel. Once he is free from Dis he will re-assume his angelic form. This will surprise him since it means the Powers the Be aren't necessarily the ones after him.
Finale - Knocking on Heaven's Door
Elniel will inform the PCs that he suspects Galriel is part of a separate faction of angels that are more hard-line lawful than good. He had heard rumors that such a group existed but since that could be considered against the will of the Powers That Be no one believed it. The best course of action to end this once and for all, he believes, is to go to Heaven itself and force a confrontation. He may lose his life for good but at least he may be able to buy Lilly peace. The PCs can come if they wish.
At the Gates of Heaven Elniel is taken into custody and put on trial much to Galriel's dismay. If the PCs are there they'll also be detained. If not they will be summoned to Heaven anyways in order to speak as witnesses.
What follows is a trial where Elniel has to defend himself. He'll profess his love and under pain of truth describe the love that Luneelle feels for him and Lilly. Galriel goes on about touching evil and crossing lines that should not be crossed. The PCs will also be called upon to testify. This is an opportunity for a player to channel Shatner and testify about the power of love to Heaven itself.
If the PCs don't Shatner it up (or fail a skill challenge depending on how you handle it) then it is decided that Elniel will be rendered mortal but allowed to live with his family in peace. If the PCs make a difference he will even be allowed to remain an angel. Either way Galriel is incensed.
War in Heaven
Galriel has had enough and gathers up a rebellion while the PCs are still around. This is massive angel on angel conflict and the PCs are caught up in the middle of it. It is their chance to go full epic, preferably with their actions deciding who wins the war in Heaven.
When the dust settles Galriel's faction will either be in charge (and the PCs will either be dead or hunted by angels for the rest of their lives) or banished to Hell to become a new set of demons. Elniel will return to the prime material plane to live out his life with his family, either as a human or an angel. The PCs will each be granted a boon by Heaven.
This is pretty much one big railroad but somewhere else I had notes on how to make things more open ended. Epic level characters are likely to have connections in powerful places so they be able to find places for Lilly to hide safely. They may decide to take other actions or not help at all at some points and that is also fine. This is meant to be an outline for something much bigger.
While typing this out I had also considered swapping the three family members genders just so that the problematic theme of "females seduce and destroy" inherent to succubi could be avoided. It doesn't really change all that much.
And yes, there is a good deal of juvenile, "fuck yeah fight the power!" underlying this. This is an OLD idea.