Logically, the only thing CloudFlare would do is lower or eliminate the free usage tier. For instance, if X million operations are currently free, they make X/2 operations free. I don't think they would do that, but if they did, it couldn't possibly be existential to any viable company.

Practically, any metered supplier can put you out of business. It usually doesn't happen because destruction is mutually assured.

+1 for using smaller, more independent companies in any case!