IPad – If you deactivate an iPad from your Apple ID, will it still receive iMessages

Your brother's Apple ID probably still has his phone number associated with it for iMessage. The smoothest way to deal with this is to have him disassociate his phone number from his Apple ID.

Apple has a self-service web site that explains how to accomplish this:

• https://selfsolve.apple.com/deregister-imessage

If that doesn't work, this older KB article has a helpful section "Unlink a phone number".

If he has other Apple devices (Mac or iPad) that are using his Apple ID, your iMessages may be being delivered there. If none of those devices are available when you send him an iMessage, your phone will eventually offer you the opportunity to resend the message as an SMS or MMS.

Unfortunately you can't disable iMessage on a per-contact basis.

If your phone gets close to any WiFi network it has been connected to before it will reconnect and receive whatever is pending (iMessages, Mails etc.). Depending on your Notification Center settings and/or the strength of your password (if any) the person holding the phone will then also be able to read them.

But

• are you sure the phone is gone and not just laying somewhere you haven't been looking at?
• you still can use Find My iPhone to erase everything on the phone (which will be executed if the phone goes online again)