The clutch is a mechanical type (as opposed to hydraulic), so the oil level wouldn't be particularly meaningful. That's not to say, however, that running the engine with a low oil level couldn't have damaged the plates.
There are several methods that can be used to break loose a stuck clutch, but since you need to remove the cover to repair the mechanism, you're best off addressing the clutch plates at that time.
Keep in mind that a released clutch is not the same as having the bike in neutral. You'll still feel a good amount of resistance at the back wheel.