Eventually the unofficial client gets "fingerprinted" and its over. Its easy to remove the suspension, though. I vaguely remember it was through email.
I got banned for trying to move my chats from Android to iOS using the app rather than the special tool I didn't know you were supposed to use. I was lucky I eventually got unlocked.
I want a decent WhatsApp client that doesn't crash constantly and where you can search properly, but it's not worth the risk of getting banned again.