Proper way to delete route domain

clean way would be to just create everything again in route domain 0, delete the configuration in the other route domains.

if you feel secure with the config in the bigip.conf then you can edit that, remove all route domain references and do a tmsh load sys config.

i would take some measures to make sure you don't end up with an unloadable config. make a UCS archive backup or snapshot if you run it virtually.