That wouldn’t be him “up to” anything.

If it was “what’s news about Michael Jackson” that’s different, but the question was, “what is he up to” which idiomatically means “what is he currently doing”

Rotting in a grave (like all dead bodies do), that’s what he is currently doing.

(well, all the PS he had notwithstanding, that stuff might outlast post-nuclear-holocaust cockroaches)