'Plan Vigipirate' in effect applies permanently. It was originally a status that could be 'in force' or 'not in force' depending on the general security situation pertaining , but I think that essentially as in the UK, Vigipirate will now be 'in force' for evermore, but just with various levels as here in the UK.
Annoyingly there does not seem to be a simple way to find out what the current level is (I've tried the French government web sight 'security' page but still no luck
Wikipedia has a reasonable English language summary:
http://en.wikipedia.org/wiki/Vigipirate