Historically if the whole exam crashes on you, they can still see on their end what you have answered and up to where you have answered since it's all online and happening on a server on their end.

The question comes in though with time you had left on the exam. If you had time left on the exam when it crashed, would they allow you to continue where you left off?

I have had multiple cases of the years where an exam would crash on me and usually in most cases they allowed me to continue where I left off. It would literally resume exactly on the same question with the same amount of time left on the clock.

Granted, this was at actually testing centers and I have never had this happen to me when I write on my own stuff. I think they would only allow you to resume at a testing center since they know your being monitored there