Do you mean the trim tab (the "plane"), itself, is gone? How the heck did that happen? I can only think of catching something in reverse or wrapping a rope around it and then the prop. But I would think there would be obvious damage to the end of the hyd ram where it attaches to the plane. If there's no damage then I guess the lower hinge pin just backed itself off? Once that happens, the plane would work itself out of the mounting hinge.
As far as causing damage - well, I suppose the worst case scenario is that it rips off the transom leaving a nice hole to allow water to pour in. Why don't you try to secure the ram down to the hinge the best you can. Maybe something like a few zip ties to snug it down (run/insert the zip ties through the mounting hinge?). If you can wedge a piece of dense foam (think life jacket foam) between the ram and the transom, then snug the ram down so it also squeezes against the foam that should be OK.
