Untouched and out of range of all cellular networks (disregarding the SIM), most likely; we don’t know how long, though.

If your phone hasn’t connected to a cellular network in weeks and is locked in a stationary box 23.9 hours a day or more, then I’m not sure I would be surprised if it becomes automatically unreachable in this way eventually — it’s becoming unreachable any time it reboots for an overnight iOS update already, right? so an inactivity reboot isn’t going to have a worse impact than that already does.

(Note that physical SIMs were discontinued in late 2022 models, but it allows you to set an eSIM PIN with the same effect.)