Aye, correlated failure is not something to be overlooked. Mistaking correlated risk for uncorrelated risk was a big part of the global financial crisis.
There are fallback mechanisms when the risk is per model provider (as in, "What if the price shoots up 10x or Claude goes down for a day" is a manageable concern), but I'd be more worried about the way all models regardless of provider have similar failure modes, i.e. that some tasks fail in similar ways for all models. In some ways, LLMs are collectively like Star Trek's Borg: you've met one, you've met all of them.
There are fallback mechanisms when the risk is per model provider (as in, "What if the price shoots up 10x or Claude goes down for a day" is a manageable concern), but I'd be more worried about the way all models regardless of provider have similar failure modes, i.e. that some tasks fail in similar ways for all models. In some ways, LLMs are collectively like Star Trek's Borg: you've met one, you've met all of them.