I removed it. Nothing terrible happened.
I grabbed the shank with some flat pliers, and then the donut with some more pliers. I twisted it with the spiral, so that it was fighting to go toward the cutting end of the bit, and it came off pretty easily. I then cut to 20mm just fine. I think it was chattering a bit more, but maybe I’m just being sensitive. I ended up with a hopping kangaroo: