a small value of slip is possible without any structural damage. and on many occasions is actually done accidentally, ie in an engine failure scenario, before the right amount of rudder input or rudder trim has been applied, where directional control is still more under control of the ailerons, than trimmed off with rudder, there is a definite amount of slip taking place .
also even when trimmed out perfectly with rudder, in the engine out flight, and a dramatic power change takes place, with a slow or intially non existant rudder counteract but an aileron application was applied to stop the secondary effect of roll, then there is again a large slip that takes place until "balanced" flight is re-attained with rudder/rudder trim.
all of this occurs without structural damage, otherwise we would be hearing of a lot more incidents/accidents of vertical stab seperation and or engine pylon seperation every time there is an engine failure.