[typhoon]

You can dance around the issue all you like, you overheated an engine.
Water in oil or oil in coolant are not the only signs of a headgasket failure. I've had more than one go between cylinders. Not all head gasket failures are sudden, dramatic failures, I bet it's been going for ages, which is a much more typical failure mode. Overheating an engine with an aluminium head that has miles on it usually fails a gasket. Since you've been losing coolant externally for a long time, how would you know if the engine has been losing coolant elsewhere?
Did you know that even a small amount of coolant missing from the system leaves the cylinder head either partially or completely uncooled, causing perfect conditions for head warpage?
Have you performed a compression, leak down or coolant gas test? No? Then get to it and check for a blown gasket.
A sensor is not going to result in a no start, hard start, misfire/backfire maybe but not no start at all.
If you have spark and a starting aid will not fix it, you have either a valve problem or no compression.
As you overheated the engine I am leaning towards no compression. I don't buy the pure coincidence/just happened to blow something electrical same time as engine overheated theory at all.
Any EFI engine will start and run if a sensor has failed (except crank angle sensor) they go into a default mode and assume sensor is dead and substitute a default value.

Regards, Andrew.