And at some point the Sun will stop burning and maybe even explode, but for us, our children and thousand more generations it won't be a problem, it's just a trivia fact. It's much more likely that in thousands of years Bitcoin will stop existing than that all coins will be lost. And if supply will ever be a problem, it's possible to split coins further - create fractions of satoshis, so that there's enough units for every need. Lightning Network allows it even today.