I've read a lot about the Bitcoin nodes and about running one myself but it's nearly impossible to download almost 500 GB of the entire Blockchain with the speed of the Internet I'm currently using. I know nodes are just simple computers running on the Bitcoin network operated by individuals and I've also learned that there are approximately 75k active nodes ( both listening and non-listening nodes) my curiosity is what would happen to Bitcoin if these 75k node operators decided to shut down.
If all nodes shuts down then everything about bitcoin also goes down. Because miners are also node runners and if all miners stop working then nobody will mine bitcoin, nodes also verify transactions which makes them much significant to the network.
So it’s Fair to say bitcoin that without node runners bitcoin won’t exist.
Except you want to run a full node then downloading the whole Block shouldn't be your problem. You can run a pruned nodes to reduce the total storage which the block will occupy in your disk space, The current Blockchain size is around 651.13 GB [1] so it's even above your 500 GB space.
Running a prune node is just practically saving some blocks only, nothing changes with full node. You will still need to download every block which is the total storage and that’s what OP was all about. Also even if you need to import an address practically a old one you will need to download all blockchain again