We have actually had that happen, repeatedly. Whether it was them being too slow to moderate malicious spam on their relay, the website going down, the relay going down...

Always resulted in a mass-exodus of people who couldn't figure out how to adjust by moving to other clients and relays.

The users with the most staying power seems to be my "generation", which arrived after the initial building phase and before Primal, so that we tried out different clients and figured out what relays and NIPs are, and stuff. It was a steep learning curve, but we're much more resilient.

It felt like learning how e-mail or SMS or telephones worked, before everyone used WhatsApp. The Primal onboarders are clueless and helpless, like the WhatsApp onboarders. If Primal goes down, they think Nostr is down. If WhatsApp goes down, they think all mobile communication is dead.