It really depends on what material the speaker cones are made of. Provided the speakers are not receiving power, and provided the cone material is something waterproof like hard plastic, then sure they will almost definitely work after having COMPLETELY dried out before being powered back on. There could be some corrosion or even rust if there are any rustable parts, and the speakers will almost surely never perform quite as good as they used to, but they will probably still work.
Now, if the speaker cone or membrane material is not waterproof (some are made of felt or a paper-like material), then they will be so damaged after going underwater that they will sound terrible. They may still work, but they'll never sound good at all.
The bottom line is that if your speakers do get submerged, you need to give them several days or even a week or two to dry all the way out. Put them somewhere like a garage where they can't get wet and there's a lot of air around them.
