Could you imagine the world in 50 years WITHOUT Bitcoin?

If Bitcoin were to vanish right now, there would be no means for humanity to recover from the coming global depression. The size and wealth of the global population depends on the current degree of international division of labor. And the breakdown of the fiat system would make such a division of labor infeasible. I won't go so far as to say it would be a dark age, but the loss of wealth (and life!) would be very severe.

Or what could be NOSTR without Bitcoin?

Nostr without Bitcoin would be like the internet without e-commerce (e.g. what it was in the 1980s). If Bitcoin were to vanish, Nostr would fade into obscurity (unrelated to the global economic troubles), to be used by a few nerds for things that don't matter. The internet/Nostr without e-commerce is an internet/Nostr without a reason to thrive and grow.