2001 x 5 Engine problem

[AL_MAX]

Thermostat stuck during a very cold day (-10deg F), car was running idle and engine stopped by itself. Took it to several mechanics, and since battery was low and still very cold, mechanics could not make the engine turn. One of the mechanics removed the spark plugs and found oil in all 6 cylinders. Mechanics declared that since car could not be started, the engine is DEAD.

Today temps reached (50deg F), the car is attempting to start, and car was able to be cranked and looks like the pistons are moving. Is it true that the engine is DEAD or is there hope that the engine went to some kind of safe mode to protect the engine when the thermostat stuck?

thank you in advance for your insight and feedback