I don't know how many bitcoin miners are currently mining bitcoin. But, I guess that the majority of cryptocurrency miners are mining bitcoin. It is expected that the last bitcoin will be mined around year 2140. There will be no block rewards for bitcoin miners after that and only transaction fees can be collected by miners for verifying the bitcoin transactions.

In order to be profitable for miners, transaction fees have to be increased by a significant amount by 2140. The issue with higher transaction fees is people may be discouraged to use bitcoin which may cause a reduction in bitcoin transactions.

Then, will it be profitable to miners to verify transactions? Will miners leave bitcoin?

I am not sure how this will work. What do you think?