Hi,
I have done the same a couple of month ago. I have done the following.
1. With the Import/Export API exported the policy to Smart-1 Cloud.
2. Created new gateway and cluster objects in Smart-1 Cloud with the same setting as in MDS.
During a maintenance window we migrated the management to Smart-1 Cloud.
1. On the standby member performed a SIC reset without restarting the services.
2. Generated the MAAS tunnel key for the standby member.
3. Connected the standby member to Smart-1 Cloud with the SIC key from step 1.
4. Install policy in standby member. Uncheck the option to install even if it fails on one member.
Repeated the steps above for the active member.
The backup plan was a SIC reset via cpconfig which will restart the services. This is also an option if you do it on the standby member first and perform a fail over once the standby member has a policy and is managed by Smart-1 Cloud.
We had a maintenance window, but I cannot recall any major outage when performing the procedure above. I am not sure this is a supported procure, but it worked for our scenario.
Didn't notice the restart of services when setting up the MAAS tunnel, but did not monitor that too closely.
Just make sure you have a maintenance window and a good test-plan. Also make sure you have control over the gateways all time via console access.
Good luck,
Martijn