Nothing unusual that airlines stop selling seats on flights before officially cancelling the flight (and sending out notices of cancellation to pax). Unless of course the flight is actually sold out?

Vueling will soon notify you. But notices of cancellation are not send out to all at the same time/at once (as it will flood the call centers with cancellation, rebooking request calls etc). I would expect you to be notified within a few weeks. So just be patient. For flights in March there should be no issue (as it is low season); you may even benefit from a lower fare,