A flame out is when your engine stops running un-commanded. It has various causes. Bad glow plug, over rich or lean. Binding on the flywheel, out of fuel. There are a ton of reason an engine can "flameout". It is only as bad as the cause of it.
Indeed....you can fly with out radar, hydraulics-(fixed wing only) and a whole lot of other things but if you want to watch a pilot pinch a plug out of the seat....start shutting down engines.