I guess it depends on the size and nature of what it hits.
I misjudged how far behind a tree I was, and flew through the tree instead of flying behind it, and it passed straight through and out the other side, with just some trimmed leaves and branches, and some stains on the props.
On another incident I actually broke a half inch off both tips of a prop when I hit a solid branch and not only did it keep flying, it flew the rest of that battery before I found out.
The computer control must have compensated the speed of that prop, and/or slowed the others, to rebalance the system.
But I sure wouldn't rely on it.
I've had much the same questions as you whenever I've been swooped by birds. If the bird hits the props, assuming the props aren't completely broken, would they regain speed fast enough for the quad to recover? I actually don't know, and don't want to find out, so I always head for home fast when birds begin swooping.