"you can not have more than 180 sub days at a time"

[Lexia]

I'm pretty sure it doesn't boot you out if your sub expires while logged in.

You just won't be able to get back in.

But you should be able to add more time, it's silly that you can't.

It kicks you out otherwise if it didn't people would just stay logged in and never log out for as long as they could stay on to avoid having to pay their sub once it ran out.