I think they bring back Dolegala on the PS (I believe he's available again) as a layer of security until Stidham can come off the PUP in 6 weeks. At that point there should be less of a roster crunch and they'll carry all 3 guys, but if they need to float someone they can probably move Hoyer to the PS and bring him back as necessary since his salary will have been guaranteed from being on the week 1 roster (assuming they bring him back today).
By mid-season my guess (or at least my hope) is Stidham would become the #2 since he SHOULD have more upside than Hoyer if Mac gets hurt but who knows.