Miners would still collect transaction fees.
And yet it is (extremely) improbable that individuals will pay many many billions of dollars/year to move money around (which is what it takes to secure the network).
The only way the network's security does not collapse is if bitcoin's value goes up faster than it declines over time (50% every four years (the halving)).
No one does the basic napkin math on this and it drives me nuts. Unless the code changes, Bitcoin inevitably fails.
And yet it is happening right now ! You should have looked at the data to see what fees are being paid :-) Looking at the average over the last 10 days: bitcoin users have been paying about 1 BTC in fees per block, so 6 BTC of fees per hour, or $8M per day, or $3B per year (yes, billion with a B): https://www.blockchain.com/explorer/charts/transaction-fees-...
I can't locate a source that calculates exact fees spent over the last 12 months, but per the chart above it seems to be around $1B per year.