Will accounts ever be made inactive due to non-use?

No.  You can upload a file onto the permaweb, and walk away from it for 1, 2, 5, 10, 50 years and it will still be there.

You will never receive a message that your account is going to be closed due to inactive use or a missed payment.

Think of it as your safety deposit box of data that you only have to pay for once.  As long as you keep the key, you can always access it.