This kind of thing is done all the time by teams that win a cup. Just look at some of the series the Preds have lost after chasing the starter early in the series. Then the starter winds up back in at some point and carries them to the cup.
I was curious, so I looked it up.
2010: Niemi started every game
2011: Thomas started every game
2012: Quick started every game
2013: Crawford started every game
2014: Quick started every game
2015: Crawford started every game but 4 (all against the Preds)
2016: Murray started every game but 3
2017: Fleury started 14 games, Murray started 9 (including all against the Preds)
2018: Holtby started every game but 1
2019: Binnington started every game
2020: Vasilevskiy started every game
Only 3 times in the last 11 postseasons has a team started their backup, had it go well enough to give him a 2nd game and then gone on to win the Cup. That's not really a good stat for justifying changing the goaltender, IMO. The majority of the time, Cup winners either stick with the same goaltender, even after losses (including losses in which the starter was chased), or go right back to the original starter after one disappointing game with the backup.
In other words, there's more justification for sticking with Saros. That said, if Saros allows 4 goals again, I wouldn't be opposed to starting Rinne, regardless of what the Cup winner history recommends, since the Preds aren't close to that caliber of teams and need everything to go right just to get out of this 1st round.