I would guess that Liberty Media did some due diligence before investing in MotoGP, and there will be a plan for a way forward. If the media income can be increased as they say it can, then there would be plenty of finance to run teams. Maybe not teams with the size and engineering sophistication of Ducati, but I think the budgets would have to drop an awful lot before there is a real loss in racing quality.
Only if it becomes necessary to save the championship if manufacturers exit, there could be a spec 1000cc engine tuned a bit to give, say, 240hp. And then allow independent frame development. So, sort of like Moto2 now but with more power and therefore speed. If Kalex and Boscoscuro can make it work with the lesser exposure (and therefore lesser sponsor finance) in Moto2, I'm sure it could work in MotoGP.
The CRT experiment was in a field that still had manufacturers. If that was returned and enforced for everyone, then I think that could work. But, I can never see manufacters being deliberately removed from the championship, so this would only happen in an extreme situation.
In terms of the future, there are electric motorcycles. But, while there are plenty of brands of electric motorcycles out there, I think they need a doubling of battery capacity from the current approximately 20kw/hr before they can take over on the road. That will happen, but it will take time. And, for races similar to what we see now, battery capacity needs to be much more.
Going way off topic here. So, to bring it back, will a situation be bought in whereby the teams make a profit for their manufacturer, as well as exposure/advertising? That would perhaps keep even a struggling company such as KTM in.