How to get in Demonis in LATER STAGE of the game?

[Aleksandar777]

Originally Posted by ByteRider

hint: Later on when you are working with the dwarves, you'll come across a quest in the tunnels regarding a demon and a love sick dwarf. You'll be able to make your way back to Demonis then.

Is it posible, when you go to demonis from dwarves, to go on same places as before and also to go in hades?
I just like to know if i continue with main quest but dont kill all armies in demonis and hades, will i be able to turn back and kill them later?