The airlines are going to have to do some comms on this. I have a Ryanair itinerary next month that specifically states T3 for departure. I can already foresee plenty of people getting dropped off at T3 only to find security shut and sent back outside to T1 (probably to join the back of a long queue). What a mess.
I highly doubt the airport will reopen T3 drop off when passengers have to go through T1 check in and security.