It’s a tricky one.
First of all, the World Gov isn’t going to fall, it’s the Celestial Dragons that will. There will be a new system, with new (and old) leaders. Bounties will still exist, because there will still be evil pirates around.
However, Luffy himself really should not be considered a criminal at this stage. All the new leaders of the world will be his friends and allies. They won’t want Luffy captured.
But there’s also the fact that Luffy... really likes having his bounty? He’d be gutted if he didn’t have one anymore, look how happy he is when he gets a new one, and how upset he was when he thought it went down. Luffy likes being a pirate, he likes being a wanted man on the run from good Marines like Smoker and Coby. Would Oda take that from him? Make Luffy a world wide hero, despite Luffy himself being horrified by the idea?
I suspect that the route he’ll go will be a psuedo-Alabasta like ending, except this time it’s Luffy himself asking that they cover up his great deeds so he’s not widely considered a hero, but more of a beloved outlaw, like he is right now. Tell Coby and Smoker they‘ve still to try and catch him if they can, picking fights with whoever he wants.
So I’d still say he will have his 5.6 billion bounty that surpasses Roger, and it’ll come after the final war.