I'd argue it doesn't depend on bitcoin. But bitcoin does certainly serve Nostr well.
Discussion
how else can infrastructure providers and builders run things without being subject to defunding?
Can someone post a network diagram of how Nostr works / is architected?
The free market can figure that out. It seems like Bitcoin is the logical choice, but if Bitcoin were to be shutdown or otherwise unable to serve Nostr for whatever reason then some other solution would be found for sure.