I believe you'd use:
SYSTEM_MODE(MANUAL);
SYSTEM_THREAD(ENABLED);
int connectionFail = 10000 ;
You would manually connect after waking from a sleep cycle, then something like this to limit the connection attempt before performing the disconnection process and going back to sleep to save battery.
if (waitFor(Particle.connected, connectionFail)) {
// do your stuff here
Note: this may change for Mesh, IDK.
For example: This is what I did for cellular, a similar concept might work for you with the proper Mesh Calls and using the best Sleep mode for the Xenon for your case: