On the last lap of the race as I was starting my attack, the guy leading out the group pulled off with his head down and almost went into the curb sideways. He looked up at the last second, bobbled and saved himself but slowed several of us down. I was far enough out that I could get around without too much issue and still have a reasonable finish. Guess who this guy was...?
In any case, a missed clip-in should be virtually imperceptible to the rest of the racers. I've been in crits where a hesitation at the start meant chasing for half the race or getting dropped altogether (luckily not to me).