We cope by saying they hire a replacement who asked for more. The reality is they generally don’t. They either offload the work to the rest of the dept and go “oh look at that we didn’t need them!” as the group drowns OR they find a wide eyed, younger professional who will take a crap - or at least lower - salary.

Which doesnt seem to be common, seeing how you have shit like the report that OP posted that job hopping massively increases income.