This is all silliness.
Sanheim wouldn't be on the team if they weren't planning on playing him, he'd be in the AHL.
This is just a couple games where they're giving him the extra work and coaching treatment, basesd on stuff they've seen his first couple games, to get him up to NHL speed.
He's going to be in the starting lineup pretty soon, and once he hits his stride, he ain't coming out.
Morin is a little different, with Provorov and Ghost on the left side, there's only one spot left, and gee, you want Sanheim in the lineup, well, he'd have to play RD to do so if Morin comes up, and they have to be confident he can handle that in the NHL. If MacDonald keeps playing well, and the team is winning, I don't think they're gonna want to bench him to start 3 rookie defensemen down the stretch run with two playing on their off hand.
But it's a long season, crap happens. So it's possible Morin comes up, it's possible Myers jumps ahead of him b/c he's RH, it's possible that Friedman who's about the same age as Morin makes a big jump.
Don't touch that dial!