Not for long. nostr:npub16c0nh3dnadzqpm76uctf5hqhe2lny344zsmpm6feee9p5rdxaa9q586nvr has confirmed they will add a fallback where the client reads directly from relays in the case of a caching server outage.
A caching server is not a bad thing, especially as Nostr grows. Primal will always be the fastest client with the largest user base. The other clients are ugly and slow.