If I finish the underworld main quest

[MAKAIROSI]

Can I come back to the underworld? The protagonist says that the Underworld is pretty much throwing us out, but we can travel to another camp to finish other stuff, and then reach the final portal.

But I'm a bit tired of it now, and I wanted to try the other dlc. So can I safely leave the underworld and come back to finish the rest of the stuff afterwards? Or is it locked after that

[N'fol]

Yes, you can go back later, from either where you entered the first time, or where you exit after completing the main quest. (On the surface area, the entrance and exit are very close, but returning to the underworld via the exit reduces the amount of under-world traveling you'll have to do.

The second DLC is the same way: after you complete it, you can return.

(You may also leave either DLC before finishing them to return to the main game, then return to the DLCs later.)

For that matter, even after you complete the main game's quest, you'll see the ending sequence, credits, and statistics, but when you load the game back, you'll be right where you were before you ended the game. (So you can then dysmantle more things and do whatever side quests you want to do.)