I've gone too hard to early quite a few times... but never had to end a ride early. A couple times I've dropped of the back, regained my composure, and then just rode solo until I caught up again (if the group hit a red light or something). A couple weeks ago we had a near-crash in the front of the "fast group" and I had just gotten off a pull. I couldn't recover from the surge of wind off the front from the line breaking up and ended up riding about 4 miles solo @ 25mph. Wouldn't have caught them if it wasn't for the rest area/checkpoint.