I assume the same would be true if, for some reason, the first three rounds went so long that the Speed-Up happened during R3 when there were still prizes on the wheel (that is, the prize wedge and gift tag weren't removed prior to the FS).
From what I understand about the show, this shall
never be the case. Even if the first three rounds take so long that it would warrant a Final Spin during R3, the show will
always "force" the third Toss-Up and R4 just to have the Final Spin at that point...and the game will be severely edited to compensate.
To put it another way, the show has four commercial breaks -- one after each of the first three rounds, and another following the game. Ending the game after R3 would require placing that fourth break either 1) after the Bonus Round, which has not been done in some time or 2) during one of the first three rounds, which has not been done in an even longer time and would result in the first utterance of "Turn your backs." in about two decades or so.
(No, I do not have the pleasure of being connected to
Wheel, either.)