Let's say Bitcoin ends up being successful and takes over as the world's main currency for thousands of years. Over time, users will of course lose some bitcoins and be unable to retrieve them. Once all of the mining rewards are distributed, the number of bitcoins in actual circulation will decrease. Theoretically if Bitcoin ends up surviving for a long^longlonglong time, there will at some point be very few bitcoins (and eventually, there would be 0). What if there becomes so few that even bitcoin's eight decimal places aren't enough (like if 1 satoshi becomes worth $1,000,000 because there are so few bitcoins and people can't even afford 1 satoshi)?

Is there any solution to this problem? Of course it's theoretical but just curious. I was reading online that eventually, if needed, it would be easy to just add more decimal places, but eventually there would theoretically be 0 bitcoins in actual circulation.