You have 2 options here.
1) For the Merge Agent job, Run agent job step, click Edit and navigate to the Advanced page. Set the On failure action to Go to the next step and create another job step 2 which runs the Merge Agent in the exact same fashion as Step 1. Then on the Advanced page of Step 2, set On failure action to Go to step: [1] Run agent. This will essentially put the job in a retry loop on failure.
2) Instead of running the Merge Agent continuously, run it on a 1 minute schedule. This is essentially the same as running the Merge Agent continuously since the continuous polling interval is a 1 minute schedule by default. This way, the Merge Agent will run every 1 minute, even if it fails. I prefer this approach personally.