Most likely you already know about the theory of the colliding miners planning a 51% attack to steal funds of transactions sitting on segwit addresses. Let's say it actually happens: Jihan and co gather and enough hashrate collides to steal segwit funds. Let's say the funds are a small amount and the address has been inactive a lot of time. Most likely the owner wouldn't even notice, or by the time he notices, nobody would believe that it actually happened, unless you can answer the question of the thread:

In the event that it actually happened, would there be any way to prove it, or it would be seen just as a regularly sent transaction?