Theoretically, if people managed to live to the year 3.890.002.012 ,?
We are unlikely to ever have such a number, so I wouldn't worry too much how to write it out. If we don't die before then, we will just keep having a bunch of new year 1. We have year one of king or emperor whoever in the past, and we might again in the future. Or we will have year one of post war whatever, or post plague, or post meteor, or whatever.