What about when it is down to 12.5 bitcoin per 10 minutes? Will people still mine? 6.25? 3.125? 1.5625?
Transactions were supposed to become more expensive, compensating for reduced mining rewards.
Possible hard fork is increasing block size by 50% a year, so that will drive transaction fees down.
The transaction cost should actually decrease over time, however the raw number of transactions should increase so the overall amount of TX fees on a per block basis should increase