There was no way around benching Fleury after the last couple of goals he allowed. He was clearly shaken and looked extremely awkward for whatever reason.
With that said, the Pens' defense has been *brutal*. No team will win a cup turning over the puck as much as they. My humble opinion is that Fleury's issues are related to the frequent turnovers and inability of the Pens to constrain offensive puck movement by the Islanders. With few exceptions, good goaltendidng is a team effort.
If DB doesn't back up benching Fleury with significant adjustments and/or benching skaters that don't make adjustments asked of them, he'll be next.