I think Honus nailed it on the head. I see maybe a high and low speed film in each chemistry type, maybe in just one frame count, not 12, 24 & 36.
I think even if Kodak and Fuji got out of it, there will still be small manufacturers of B&W film in bulk rolls.
Didn't Kodak in the last few years make a new B&W film plant in Mexico. Even if they lose money, they'll sell off the assests, and someone will probably buy it at a price that will allow them to meet the current demand.
The worse case scenario is a lot fewer emulsions, no new technology, higher prices, maybe stock outs due to a company running only one film at a time through production.