Won't it be cheaper to launch on starship than anythign else even for very small payloads? Yes, I know about RocketLab but I wonder if they will be able to survive once starship is up and running.
Russia tries to develop new rockets, but so far it's really slow and quite expensive. It's possible that when NASA will stop paying for Soyuz transport to ISS, it will become even slower. It's not a particularly good time in Russia for new rockets paid by the state.
Probably not. It's possible to bring the space industry to the state of aviation industry, but 1) some resources are still available to maintain some level (as you mentioned) 2) to keep the same level, one needn't spend too much effort and 3) there are some interested parties in Russia which wouldn't want too deep degradation of space industry (e.g. periodically some hints to that come from Samara).
So a likely outcome could be maintenance of some expertise, at least for military purposes, and possibly attempts to cooperation with foreign partners - China, Europe etc. No total destruction; "just" - potentially - another deep crisis.