How long can I be inactive?

I don't play MOP for a few months and I have lot of chars there. I dont have MOP client on my PC. How long can I be inactive till my chars get deleted?

Your characters won't be deleted O-o

I been inactive for nearly a year and was able to keep my characters.

Ok thanks <3

You can be inactive as long as you want. The only possible way to lose your character is when they merge realms and you don't, but there won't be anymore merges as there's no more realms left to be merged, but damn that's still 3 times more realms than what molten initially had at launch, so it's still a win for them.
Kinda sad to see Cata and MoP realms dying, but oh well.

if your a premium user your fine. only non donors can run into issues if warmane does an inactivity cleanup. mind you i only remember them doing 1 cleanup in the 5 years i've been here. and i think it was characters not active for 6+ months. it may have only been names that were removed as well, can't fully remember.