DM Advice: Player want to destroy Treshold

[Ivalios]

Greetings folks,

My group of players have made it all the way to the end and are looking to destroy the tower, outright. One of the players has singled out Mythic Earthquake as a decent means to that end.

I'm looking for ideas to manage/provide an outcome while still somewhat preserving what's supposed to occur (minus some of the encounters if required, because the tower crumbling down might cause difficulties for certain denizens)

Any thoughts/suggestions?