We have been taught since childhood that numbers don't end anywhere, they go on till infinity. So, mathematically it's impossible for numbers to get end. So, is in the case of wallet addresses.. And wallet address comprises of alphabets too , so it's currently in near future tough for them to get finished.
But, even though it happens in future, simple solution is increasing or decreasing number of digits. But, currently it's not a matter to really think upon.