Removing the primary server does not make the secondary the primary.
If you are concerned with continuity of services while undergoing the move to a new domain/ip-range, you could consider leaving both the primary and secondary policy servers in place for the existing domain, and installing new policy servers (new policy group) in the new domain. The sudo plugin hosts could then be moved at their leisure by unjoining from the existing policy group, and then joining to the policy group in the new domain. Once all the plugin hosts have been moved, the old policy servers could be decommissioned.
The other option would be unjoin the sudo plugin hosts then remove the primary, and then rejoin and follow the steps in the guide for setting it up as a primary. Then do the same for the secondary. Then join the sudo plugin host to the newly setup policy group.