The escape through the self-destructing villain's lair is a classic element of films going back as far as Dr No, the first James Bond film.
When a hardy group of PC heroes successfully infiltrates a dungeon and defeats the final boss, try having the dungeon start collapsing around them. Mooks and minor monsters can scurry and flee all around them. The heroes' priority should be to get out before the place caves in and lava fills all the open passages. Fun and excitement for all!
GM: Luke, the whole station around you shudders and alarms go off.
Luke: We need to get out of here. The Rebels have started attacking.
Darth Vader: Leave me. I'm finished.
Luke: You can't die!
Darth Vader: I know, but...
Luke: I'm taking you with me.
Darth Vader: Why do you even want to save me?
Luke: You can redeem yourself, turn good again.
Darth Vader: I can't. It's too much to ask. I was too close to Anakin for too long. He corrupted Palpatine, he corrupted me.
Luke: You can be good! You can follow the Path to the Light Side of the Force.
Imperial Trooper 1: Did you hear that? No more Force Chokes!
Imperial Trooper 2: Yeah, just Force Smother to Death With Kindness.