I think that just speaks to the very plausible rumor that Alonso is contractually obligated to let Ferrari make their own driver lineup announcement before he's allowed to make his own. McLaren was always the obvious option.
As far as Mercedes, I think that was certainly a possibility, but that's more in the hands of Lewis. If he was losing to his teammate right now, he wouldn't have the team support nor the leverage to ask for the money he's looking for. Remember, Mercedes had been talking pay cut for him, and you know that wasn't going to fly. They'll pay him if he wins however, and that's exactly what he's been doing. Essentially squashing the idea that he might leave, closing the door on a potential open Merc seat.
The whole paycut debate has been entire driven by fans as far as I've seen.
Top teams don't give top drivers pay cuts in any sport.