This is regarding your 2nd point.
1. If there is redundent link configured. The messages will be transfered in the redundent link.
2. In casae there is no redundent link. in case of SAM or CPG you need to start timers monitor them. In general some stacks will automatically start timers for the same. if the timer expires it will send REL (on both sides) to ur application and to the network.
Thanks and Regards,