I've had flights cancel on short notice due to no captain. Last time, I called scheduling before I left home asking if they were going to find a captain for my DCA turn. They said they were trying to find someone. A little while later (after I shaved, of course), I look at the pairing and see we're cancelled.
I have a flight tomorrow that currently has no captain. We'll see where they go with it. Edit: looks like they found someone.
The big problem right now, believe it or not, is that we're short on captains. Now that we're getting new hires we can upgrade, but there's a lag due to having to send them to training. Right now they're prioritizing new hires and CRJ transitions for sim space, which is probably why we haven't had the next bed drop yet.