Fork it while you can!
forking is just a gesture, especially for obviously hot repos. a takedown of 1 can takedown all the forks
Even as a "backup", it's pointless, because it's all Copy-on-Write, there's no backup.
As if they never learned to use the "Star" button to bookmark...
Personally, I don't fork any repos unless I'm working on a derived program, or working for a patch, even so, I'll delete my forked repos as soon as the patches are accepted (if it's a one-time contribution), so these forked repos won't spam my own list.