I thought it would be helpful to pass along my learning's relative to the array evacuation process. As an array needs to be removed from a group, certain steps may need to take place. I have listed some my thoughts below:
1) Define which array manages the leader role of the group. If the array leaving the group holds this role, work with Support to migrate this role to another array in the group.
2) The array leaving the group cannot be the only array in the default pool which cannot be empty or removed from the group. Move this array into is own pool along with the leader role being re-associated
3) Migrate all volume to the other pools thus removing volume ownership of the array to be evacuated
4) Ensure all data connections are maintained with the other arrays in the group. Perform a health-check with Support prior to evacuation to ensure data path connections will maintain connectivity.
I hope this helps shed some light on the process if you are in need of this process.