Scherbak's stint still has another 6 days before the have to bring him back to Montreal, which would fall on the 13th. Laval has 3 games until then, with a 4th one on the 13th (I don't know if he can get to play in that game, but I doubt it). With Scherbak having played one game sick and the other one not being able to finish it, it "delayed" any possible early call up.
We shouldn't take this as the Habs no longer having faith in Scherbak.
As for Agostino getting the call up, he's the team's best scorer. And he was among the last to get cut at camp, so we knew that he'd be a very possible call up.
I prefer calling Agostino up than any of the young kids who need playing time in the AHL, Scherbak included due to the circumstances of his stint and being sick.
If McCarron wasn't injured, I believe he'd be the call up.