Baldur's Gate 3

Well, I got super curious back in Act 1 and remembered him telling me once about his original plan for when it became too unstable to handle anymore, i.e. to find the deepest, loneliest part of the Underdark and wait. So I took him down to the lowest point of the forge that I could find, slaughtered him, and then made haste to whatever point of the map was both topside and the furthest away I could possibly get before continually long resting, just to test if it actually would go off in-game or whether that threat was set dressing.

Nah, it still insta-kills you when the clock runs down. Just completely wipes the entirety of the coast, I assume. He mentions around the end of Act 2/beginning of Act 3 that he doesn't want to kill you and hopes you could find someplace safe away from him when he does so, but judging by that, there's nowhere far enough that you could possibly run. Fucker's "glorious sacrifice" is going to block out the sun for years.