I have a similar situation with my Catalina 320 wing keel. Due to wind, the boat moves about in its slip and rocks a bit from wind generated waves or passing boats. This movement will cause a hole to be washed out over time in soft mud, so when the boat actually bottoms out, if it settles into the mud, it is not likely to be as deep into the mud as you expect. Your sailing performance might be affected since some mud can rest/stay on top of the wing. I think the rudder, being flat, will just push down in the mud a bit. Gradually, as the hole gets washed out, the times, even in low water conditions, that you are actually aground will be greatly reduced. A down side, is even if the boat is floating in low water, you cannot go sailing since you can't leave the slip. My boat has been in the same slip since 1999 and I have seen no problems. In my marina, there are numerous other sailboats experiencing the same thing and I have not heard of any problems created by this situation.