Dude, do you realize how many addresses a 128-bit address space gives you? About 3.4 * 10^38 address, give or take. I would type out the number for you, but I'd probably get carpal tunnel syndrome from doing it.

If you were to assign addresses at the rate of one billion addresses PER SECOND for a BILLION YEARS, you would not even come close to using up one trillionith of the address space.

In short, we will not 'run out eventually', as you say. The sun will supernova long before that will ever happen.