When in doubt...
If you're unsure if it was a "simple" flameout or a severe damage, then treat it as severe damage.
It's best to land with a good engine shutdown than to try and re-start an engine with severe damage.
IMHO 0 N1 is a good sign of a seized engine. N2 may slowly wind down to 0 at low airspeeds, but N1 should always be rotating simply by windmilling.