With Prius batteries, there’s a whole refurb scene where people buy the whole pack, crack it open, find the underperforming cells, and replace those. And that’s for a very small battery. So I would guess the same will be done for EV packs, since “most of the time” the cells will wear unevenly and the whole pack won’t be bad at once. If you do need a pack replacement after 10 years though, you probably get more power and range and lighter weight, so you get an upgraded car at the same time.