The PBS MOM process is the parent process of the PBS jobs on it's service node. You can kill the pbs_mom and the PBS jobs will continue executing. But when you restart the MOM you must start it with an argument that tells it to monitor the running PBS jobs. Otherwise it will kill them.
To stop the pbs_mom:
kill -2 {pbs_mom process ID}
To restart the MOM so it will monitor the running PBS jobs:
pbs_mom -p