Im not saying we will stop using bitcoin at 2039, im just saying a huge ammount of bitcoin will be mined at 2039, soo we have some more years to have some solution about miners rewards.
Not really. Except the fact that mining rigs will cost A LOT for the required speed it will have, the block reward and mining time for a block will be changed: the reward will split every 4 years and the time will keep going up until it's probably going to be impossible to get one Bitcoin a month. By 2039, if everything will be right and Bitcoin will still be used, it means the price will have to be OVER $100K for it to resist.
By that time the miners "reward" will mostly consist of miners fees, which you evidently forget about here. Right now, they amount up to a few percentages of the reward for finding a new block. If the reward is gradually halved down to zero, in order to keep the miners profits at their current level in fiat terms, the Bitcoin price should increase a few dozen times. On the other hand, if the block size gets increased, more transactions can be included in it and thereby more fees can be booked as miners profit. But even if neither the price nor the block size increase in due course, mining won't stop anyway...
Since some miners will start leaving while mining difficulty decreasing, eventually making mining profitable again
