Personally I think NVidia would make an exception here, the Nvidia-Nintendo deal was around a decade in the making, originally they'd planned to collaborate with the 3DS but NVidia couldn't get the power envelope or costs low enough, NVidia has thrown a lot of money at trying to get Nintendo design wins over the years for whatever reason. As well as that, Nintendo I think have said repeatedly now that their plans are for the Switch to have a >10 year life cycle(A feat they managed with the GameBoy and DS lines) with upgrades, so that implies both new silicon, and backwards compatibility, which of course heavily implies they'd have to stick with NVidia but get a new part. (Also the Switch is a proven success at this point, and every Nintendo handheld line before has sort of had upgraded mid gen refreshes(GBC, DSi) and then spread into a semi separate 2nd gen(GBA, 3DS))
Though saying that, Nintendo has historically also been fond of providing backwards compatibility by just sticking the old chip in along side a new one, if that was economical.