It was not the floats that "caused" any control difficulties, it was the complete lack of an anti-torque system, and the fact that the pilot slowed down, so that the vertical fin/endplates were not sufficient to make up the yaw control gap.
It is possible that the pilot could have flown to a landing, since the fin is capable of sustaining level flight under some gross weight conditions in a fenestron aircraft. Second-guessing the PIC here is a pretty lame thing to do, especially when all came out of it well.