If Bitcoin adoption(and price) continues to increase as time goes, this should be enough incentive for miners to continue mining. And knowing that it's estimated that year 2140 is the year where almost all bitcoin has been mined already, that's more than enough time for Bitcoin to have enough adoption.

In the end, time will tell. And unfortunately we wouldn't be around in 2140 to see the results. All we can do is to have enough bitcoin for our children and grand children so they can reap the fruits of our labour.