Is "go out, stay out" always cast in concrete?

[Dakota]

3 umpire game. Runners on 1st and 2nd. Low fly ball hit to shallow left/center; too high to be called a line drive, but could be trouble. U3 turns and takes maybe 3 steps to make the call on the fly ball (not caught). Runners now forced while F7 chases down her miss. Close play at 3B, but F5 is straddling the bag (not in contact with it) even though the throw beats the runner by a step. U3 has turned back to the infield and is literally in prime position for the call while PU is still moving into position.

So, cast in concrete? Or, can U3 communicate "I got it" and take the call?