Morrus said:
Some great ideas here. I agree that searching for the child shouldn't take too long. I kinda like the idea of the "trying to find the way home" campaign, although at those levels, players have access to magic that can do it fairly easily.
I don't know about your characters, but mine don't like "trying to find a way home" plots, as I discovered when I DMed some Ravenloft adventures for them. And as you said, characters of that level are very powerful, so forcing the characters to stay where they don't want to be will feel wrong somehow. At these levels and upwards, adventures should be about what the characters
can do, and not what they cannot do...
How about some sort of "planar invasion"? That can keep the PCs occupied for a long time, and if the stakes are high enough, the PCs will be highly motivated. But they will still be able to decide on their own just
how they fight the invasion...
Mind you, I'm not talking about an invasion of the
Material Plane by otherworldly forces - though that can happen as a side effect, too. I'm talking about an invasion of the Outer Planes themselves! Some sort of cthonic entities (read Call of Cthulhu for inspiration) have managed to gain access to the regular multiverse, and now they attempt to destroy/transform the regular planes - with disastrous consequences for both Man and God.
For this you need:
- Some vague descriptions of the prime powers behind all this - these entities should be at least godlike in power, and very, very alien.
- A large array of interesting minions of various sizes and powers (best come up with some appropriate templates - this will make things easy).
- Some human worshippers and other people who want to help these entities for their own reasons. This is important - you can fear otherworldly entities, but you can't
hate them. But if there are some human followers involved who will sacrifice their own kind to help these entities destroy the world, then then you have a few villains whose eventual death will be
really satisfying for the PCs...
Just let the PCs come across some early outbreaks and come up with a reason why the gods can't do all the work of fighting the invaders alone...