Batteries are swapped all the time in the Prius world. I think it's a couple grand for the swap. Some companies even do the swaps with mobile mechanics. That being said, any of these rigs can run ICE-only without the battery, but performance and MPG will be diminished.
As a Toyota hybrid owner, it's really not a big deal to me. It's really no different than other long-term maintenance requirements for the older rigs. Like a timing belt on a 2UZ-FE or a valley plant coolant leak repair on a 1UR. It will eventually happen and it might cost a few grand, but then the rig will be good for another 100-200K.