A lot of it depends on the how they are flying . Flyers using wings will generally be of the sort that when disable will fall. Magical flyers generally don't suffer falls even if the magic is dispelled but simply float downward. See the Fly spell and skill description of Fly (I'd link but out of time for now)
They don't suffer falls if their magic is dispelled, but they do suffer falls if they're paralyzed and can't undertake the physical movements required to maintain even magical flight. It's covered in the FAQ.
Flight and Magical Flight: Can a paralyzed or stunned creature keep flying with magical flight? Does a creature with magical flight not apply bonuses or penalties to Fly checks because it doesn’t have a “natural” fly speed? Does flying make a creature immune to being flat-footed?
No, any creature that loses all actions can’t take an action to attempt a Fly check to hover in place and thus automatically falls. That includes a paralyzed, stunned, or dazed creature. Magical flight doesn’t act any differently, even for paralysis, as it isn’t a purely mental action. A creature with 0 Dexterity can’t fly, and paralysis sets a creature’s Dexterity to 0. Despite the fact that the Fly skill mentions that bonuses and penalties from maneuverability apply to creatures with natural fly speeds, they apply for any fly speed. If they didn’t apply to creatures that gained flight artificially or through magic, then those maneuverabilities (like the listed good maneuverability for the fly spell) would have no game effect. Finally, the statement “You are not considered flat-footed while flying” means that flying (unlike balancing using Acrobatics or climbing) doesn’t automatically make you flat-footed or force you to lose your Dexterity bonus to AC; it doesn’t mean that flying makes you immune to being caught flat-footed.
/cevah