99.21875% will be mined in 20 years time. If electricity isn't very cheap by then and/or if bitcoin isn't worth hundreds of thousands of dollars, it's hard to imagine anybody wanting to mine then. How will transactions then be verified?
At that time the block reward for miners is somewhere at 0.390625
BTC which is pretty low comparing with today's reward. 20 years from now the price should much higher to see miner still mining.
At that time, the transaction fee will be more than 1 bitcoin. The transaction fees in some current blocks are already more than 1 bitcoin.