I believe avax has a reward distribution schedule which governance can alter if needed. But the reward pool won’t be exhausted for decades but it’s also not a fixed supply in the way you might think. The supply is capped not the minted amount so I believe if it ever came to it, burned fees could be reissued as validator rewards as long as the supply is not over 720M. But I mean we’re talking about things very unlikely to happen. You’d need everyone staking 100% of avax for year long intervals to hit the cap due to the way the minting algo works afaik at least that’s what I gathered from skimming the white paper