Self-destruct's ability causes the server to cease to exist, which immediately ends the run. Thus, effects that last during the run like RSVP stop being active,:Ruling and end-of-run abilities like Stimhack trigger immediately before the trace.:Ruling
Only one Self-destruct can be used per run per server.:Ruling
If a runner has passed and not broken RSVP during a run. If Self Destruct is rezzed and used can the runner spend credits? The Runner can spend credits since the run has ended under current FAQ; the server no longer exists.
Take next step, if Self-Destruct ends run, does Stimhack brain damage happen before the trace? After? Where? Timing would matter in case with use Stimhack, 1 card in grip, Ekomind and Deus X in play. The Stimhack would resolve first which would mean you couldn't use the Deus X.
If I have two (or more) Self-destructs in the same server, can I blow them up in a way that the runner takes more than 3 damage? Correct! [No once triggered a paid ability must fully resolve. 1st SD would trash other while resolving]