Once I go to Deep Caverns (possible spoilers)......

[ChaunceyK]

I got the impression during the Tchortists/Faceless battle that I should hop on the elevator as soon as it arrived and descend.  Now that I've been down in the Deep Caverns for a bit, I realized how little I feel I explored Upper Underrail.  Is there any way for me to return to UU (aside from loading an older save game) or am I now stuck here?

[mattu]

You're stuck. No going back until you're done with DC. Rewind to an earlier save or make the best of it.

[ChaunceyK]

By your wording, you mean I can go back after I deal with DC? Or is there like an option to continue wandering around after the end of the game?

[Tamior]

By your wording, you mean I can go back after I deal with DC? Or is there like an option to continue wandering around after the end of the game?

Yes, there is.
However, going into DC unprepared might be a less-than-stellar idea in and of itself (depending on your build, really).

[ChaunceyK]

Well, as much as I'd like to roleplay "these are the decisions my character made and the consequences of those results," I also don't fancy missing out on stuff I could've done & being better prepared for the end.  I'm going to reload.