If the top ring & ring lands of that piston has died you should be able to see that through the spark plug hole. It will also have a lot of blow-by, take the hose off the filler cap & see how much puffs out. Does it look like a steam train? You could drive it like this if you have to since you would likely need a replacement bottom end.

If it's a burnt valve, you would hear it in the exhaust. Fix it before bits from the dead valve destroy the bore.