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.
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 so it's even above your 500 GB space.
Additionally, It's practically impossible to see all bitcoin nodes shut down. For something if this nature to occur then all network or internet has to be off before we can experience all nodes down.
Basically what we are talking about is around 75,000 active nodes running, so if your node is down someone else node is still running that's how it works.