FOP2 does not modify the dialplan or call behaviour in any way. You could achieve a failover to a 2nd number using followme or similar settings in FreePBx or the asterisk dialplan. In the case of FOP2, if you initiate a supervised transfer and you want to cancel it, you do it using your phone keypad, not with FOP2 itself, the disconnect feature code is usually all that is needed to cancel the atxfer action, but again, that is an Asterisk configuration (Features.conf), not related to FOP2 itself.