Depends on the architecture.
With 4-digit AP, if WLANs are set to local bridging then you shouldn't see interruption even if all controllers are offline.
With 3-digit AP, there will be an interruption while the AP adopts to the other controller. First the standby controller has tor realize that the primary is gone and come online. Then the AP has to adopt to the new controller. So this can all take several seconds. Solution is to use 4-digit APs

And wow you have 4 RFS in a cluster. Who sold you that???