Two possible outcomes:

- They miss their next payment and the contract is terminated. The arena owners find a new sponsor.

- The naming rights are considered an asset of FTX and are sold off during bankruptcy proceedings to recover cash. The buyer puts their own name on the arena for the rest of the contract term.

Considering naming rights are sold for such lengthy terms (20 years in FTX's case) it is incredibly common for companies to go under or get bought out in the middle of it.