I don't get it either. DS's dad moved and hour and a half away, from a place with tons of jobs and commerce to a place literally in the middle of nowhere with no job opportunities.
The situation sucks for your SS for sure, it must be hard to have a parent that is so unreliable like that. If I were you I'd wait to figure out any visitation details or schedules until the BM knows what they are doing, if they are moving, etc. All you can do is see what you are working with when the time comes, ya know? As for your SS's birthday Friday could you maybe do something big at home to take his mind off waiting for BM? I don't know how old he is though, and older child wouldn't be that easy to distract.
And FWIW it's my opinion that the person moving away cannot use "we can't afford gas" as an excuse. It was their choice to move away, knowing how far it was and knowing how much gas costs.