De man x11vnc
-shared
VNC display is shared, i.e. more than one viewer can connect at
the same time (default off).
-once
Exit after the first successfully connected viewer disconnects,
opposite of -forever. This is the Default.
-forever
Keep listening for more connections rather than exiting as soon
as the first client(s) disconnect. Same as -many
Então, você provavelmente deseja -shared -forever