'Land 3' annunciated > 500', fault detected in flare mode, will revert to 'Land 2'.
Then at 500' if flare fault remains, 'No Autoland'.
However this sequence will only be initiated once 'Land 3' is annunciated on the AFDS.
'No flare' then at 40' RA is a simple TOGA procedure. Provided of course(and this is a very important provided)the PM catches it AND announces it on time.
With ground effect altitude loss is about half the height at which GA is initiated. Therefore you still might get away with no tailstrike(especially on the -300 variants),if GA initiated exactly at 40' RA(impossible humanly).
But there is a very very small number of things that can go wrong in the flare mode IF the AFSEM has not annunciated 'No autoland' by 500'. There ARE some component malfunctions that still can't be caught in a fail operational system for a no flare fault. But they are very very few and can be counted on the fingers of one hand or less(the failable components that is).
Hope I managed to make some sense.