If the premise contributing to the conclusion to run their own chat service is:
> But Signal is still one company running one service. If they shut down tomorrow or change direction, I’m back to square one.
Aren't they in the same boat now with Cloudflare and Let's Encrypt?
Yes, probably but they are “easily” replaced. More easily than Signal in any case.
Also if we go down this road, we’re all depending on our internet access provider at the very least too! At some point we gotta know when to stop trying to be fully independent from the rest of the world. He chose there.
There are obviously other CDNs (or whatever Cloudflare considers itself to be these days) and other certificate authorities. They are all interchangeable thanks to open protocols (HTTP, TLS/ACME in this case). Contrasted to Signal: there are no other implementations.
Re: Signal, it's even worse: they are openly opposed to federation and to letting alternative clients use their server. They demand control and obedience, which has always been suspicious-enough to defeat any goodwill effort on their side. Why would I have/want to trust them when XMPP is a viable federated alternative?
Not really. If their own their domain, then it's possible to swap out CF and LE for different companies.
That would certainly be a very annoying event, but not an unrecoverable one.