Really, they've been lucky so far. I used to live near a river, the ducks usually hatched 6 to 8 chicks. But over the weeks, the numbers were gradually whittled away. Some 'families' were completely wiped out - none left. Usually, it got down to 1-3 surviving before they got so big you couldn't tell them all apart.
Nature red in tooth and claw.
To answer the Q, they would probably be OK, yes. It depends upon whether they have been relying completely on hand-outs (which is unlikely) or been getting food for themselves as well.
There may be initial squabbling, but they'll sort it all out.