Loss of coolant means that the engine would start to overheat and eventually seize up, i.e. stop running.
Depending on how much or fast the coolant was leaking would cause the the engine to seize sooner or later.
This example ran for about 15 minutes before the engine seized. Book page 54.
https://books.google.com/books?id=oU...engine&f=false
This one says only a few minutes, but goes into some detail on what is happening. Starts on book page 143.
https://books.google.com/books?id=OP...engine&f=false