Nintendo basically stuck with ATI/AMD for close to that long. Nintendo is not stupid enough to build the tools with Nvidia to support Switch to suddenly start over with someone else.
If Nvidia don't produce a decent chip, I can guarantee that Nintendo will go elsewhere. Potentially there may be an Nvidia laptop chip they can switch to, but that wouldn't be a direct Tegra replacement either.
Mobile chips are mostly compatible with each other (it's all just Vulkan toolkit, there isn't really an Nvidia-only toolset these days). Nintendo could look to Samsung or maybe a custom ARM Mali GPU - those guys have the mass market to do R&D. Nvidia never built a marketshare in that space - I always assumed that they just gave Nintendo a good deal to cut their losses on Tegra...