Power up a backup Gateway node
Since it's not possible to run a node code if the node is not connected to a gateway, it's especially important to have a backup gateway.
It's reasonable to power up a backup gateway (and power down "main" node) if the main gateway is not responding after period of time.
In general, it's easy - we need to have a dedicated node which "pings" the gateway and once it doesn't respond -- it should power up backup gateway + power down main gateway. The problem is, the dedicated node code (in loop procedure) won't start if the node isn't connected with a gateway (see link above). How to overcome it, any ideas?
I have thought about a secondary gateway as well.
In this situation, you may want to opt for your "monitoring" node to not be part of mysensors, but independent of. You can still use RF to send messages to the gateway and have it respond and turn on/off relays. But I have always found it's better to separate your monitoring from the stuff you want to monitor.
I guess it will require MySensors code modification, right?
That I am not 100% sure of. I would guess yes, but would think minimal. I would think the more troublesome area would be on the monitoring node, simulating a message to mysensors.