I would have voted for both 1st blowout, AND injury . . . but voted 1st blowout as that means the coach has to actually pull him out. An injury is an injury, so obviously if he can't play (or could play but isn't 100%), it's a much easier decision.
But I think at this stage, with the stakes high and an even series (although Pens probably slightly outplayed at this point), it'll only take one big loss for the change.
I'm inclined to agree with you Slozo, I think one blowout and he'd take a rest. However, I think Fleury would play the remainder of that game (or the all of the next game if Murray happened to finish the 'blowout' game) and they'd go back to Murray the next game. What I mean is that Murray is now their number 1 and it would take multiple blowouts to see Fleury regain that spot from him.