Hmm if u talking about content, of course KR is far way superior (from my perspective) (No event yet)
If u talking about population, there are a lot of people moving from IDN server, some went to NA or KR or JP though. Channel has been added from 4 channel to 10 channel.
We got draconian, theater reverse for punching the fly king with master of grab woffman recently, also with cutie Seth (No SA yet).
So i will answer ur question, "is it worth to come back?"
Well.. Yeah, but no event, only grinding for new equipment, just boring but important stuff.
If u lazy and want latest content, then nope.
Up to ur choice, this is just my perspective and i'm still new here, around almost 3 months cuz IDN dead.