So now it's finally time. for them to begin returning to the planes. And start really digging deep.
Weve been to the feywild, and a bunch of pocket dimensions. Also the plane of fire. But now things can really get interesting.
I don't have a clue what the framing, narrative, or theme is at your table so take what I'm about to say with a grain of salt. Also, my comments may be self-evident or completely irrelevant for you and your players.
For Epic (level 21+ characters) that, inevitably, spend a lot of time plane-hopping, I'd caution you against allowing them to directly challenge, or more importantly kill, gods. LOTS of players talk about wanting to "Kill a god." I've seen that kind of thing in far too many games and in, some, published material.
However, the reality is that gods literally cannot be killed by players. Even a party of level 30 bad-asses in the best gear available wouldn't stand a chance. To put it in to conceivable, physical terms -- It's still a contest of a handful of ants versus an elephant.
That said, gods do have avatars that CAN be killed. The avatars represent a fraction of the god's power, but an avatar is still an incredibly powerful physical manifestation of the god. And, depending on the gods rank in the pantheon, they can have several avatars spread across the planes. Those avatars are often what characters encounter (mistakenly thinking the avatar IS the god), but killing an avatar is little more than an annoyance that will do little but anger the god. Gods can replace an avatar in a month to as little as a day, depending on tier.
There are only a few ways to actually threaten a god existence and, essentially, none of them are feasible for players.
Last year I spent several months framing a campaign centered around players trying to 'kill' a god by undermining the entire faith while simultaneously building the following of a competing faith/god to take the place of the 'fallen' god. I've still got that one in the oven, but it's going to take a lot more work from me.