I actually wouldn't be worried in the short term for exactly this reason. Microsoft has legal access to GPT-4 and is allowed to host and serve it via Azure. If OpenAI somehow tanks its API in the near term, MS is sitting on a gold mine and will make use of that by continuing to serve it. In the long term I am worried, but less worried if Sam and Greg form a competing co to continue to build.
Though my investment will be still tiny at the moment, but not other multi-modal model on the market right is as good.