ChatGPT Plus was never intended to be OpenAI's main revenue stream. The real cash is in the GPT API, which they're currently making good money on, but which also directly competes with a GPT API offered by Azure.
OP might have a point: if OpenAI declines, devs might prefer the Azure API over the OpenAI API for factors like stability, quality, response time, better integration with existing Azure stack, etc.