[FredZarguna]

Well, a) he could get away with it if it were very close obviously and of course b) he can always trust his luck the the fielder will drop the ball. I can't think of a circumstance where he wouldn't have to if the ball ends up being caught. Even with the IFR, the runner may advance at his own risk [not bloody likely] but as I read the rule he still has to tag even though the batter is already out.

[Delta Dawn]

Tagging up is required from the first touch of a flyball by any fielder.

This means that if a fly ball is juggled in the outfield by a fielder and is eventually secured by the fielder, the out is recorded.

The runner however may advance after tagging up from the time that fielder first made contact with the ball.