A plane crash can make it easier to claim an alive man is dead as there may not be a body.
I could see this as a means to keep Wagner troops loyalties in check, or just to keep everyone guessing. The most likely scenario though is that Putin did what Putin does which is assassination.
I think its equally likely he was shot down/plane sabotaged, this is fake face saving thing, or the plane crashed due to shoddy mechanics. Whatever the case, the uncertainty works out in Putin's favour.