I'm correcting you because it won't be in 2100 but in 2140 when the last bitcoin will be mined, but as you rightly say, by then we'll all probably be dead, and I'm not going to worry about what happens long after I die.
The OP could also be referring to this happening before that date due to insufficient supply, with many HODLers unwilling to sell, but this would be solved with price increases.
I don't live long till either 2100 or 2140 and those years are not in my mind at all.
With what Bitcoin is designed and its growth since 2009 as well as solid foundations it has, I believe that its adoption, value and price will continue rising. This is what I know, hopefully it will not be incorrectly, and with which I have strong belief in Bitcoin future so I decided to invest my money in Bitcoin for long term accumulation and investment.
As said I won't live till 2100 or 2140 so my investment plan is not for such years and next 3 or 4 market cycles are my target time to take profit and retire with financial freedom.