Take a look at the Trigger node. It can be used to send a message if it doesn't receive one within a configurable time interval - exactly what you want.
Configure the node to send nothing when a message is received, then wait for 25 minutes (or how ever long a grace period you want to allow) and send (whatever payload you want).
The key part is to tick the box extend delay if new message arrives.
Or maybe look at the problem differently. Rather than send nothing on first message send the “It’s working” messages. Then extend. Then send “it’s failed”. After the correct timeout. Tat way as soon as it starts again it will send working.