What was Uzzah supposed to do?
Let the Ark fall to the ground?
Yep, let it fall. The predicate was all wrong: the ark was mandated to be carried by humans using the poles, not hauled by oxen on a cart. Uzzah was the unwitting victim of David's carelessness with, and disobedience of, Scripture (a tragic theme to be thoroughly detailed in the aftermath of his not dissimilar failure with Bathsheba). Uzzah should have informed himself about the Ark's rules and obeyed.
Indeed, David compounded his malfeasance by hilariously assuming the fault was with the Ark, rather than with himself--who doesn't do that?--and abandoning it (!) at Obed-Edom's Drive-Thru Discount Ark Repository and Pleasure Parlour, when all that was really needed was READING AND FOLLOWING THE DIRECTIONS.