3 man rotation question

[DTQ_Blue]

Playoff time, we're working 3-man. Runner at first, we are rotated, I'm U1. Batter sac bunts, and is out at first, and while that is happening, the runner notices that 3rd is left uncovered and never stops, going to third like bat out of hell. I pause my out call long enough to make sure that F3 isn't going to drop the ball and the runner is nearly to third when I notice where she is. U3 is at second and PU is at third where he should be. Runner makes no attempt to go home, but if for some reason she did, I was nowhere near home plate. So normally in 3 man, U1 rotates home when PU rotates to third, but, U1 doesn't normally have to stay near 1B as long as I did. Any thoughts on covering that play?