We will all probably be dead when this happens, but are there any thoughts on what the future will look like once every last Bitcoin has been mined?
Does BTC just end? Will transaction fees be enough to incentivize nodes to keep working?
there's no point dwelling on the year 2140. the mining reward algorithm approaches the hard cap tangentially, so the vast majority of bitcoins will already be mined hundreds of years before then. after less than 3 decades from launch, the emission rate will only be ~0.39 BTC/block. (it started at 50 BTC/block)
so we should see the effects of this diminished inflation a very, very long time before 2140. and re what will happen, the answer is
we don't know for sure. but the fee market appears robust and we've already seen blocks in the wild where transaction fees > block subsidy, so that gives some hope that fees will be sufficient to incentivize adequate miner security in the future.