I would strongly recommend talking with Datacore support first as they will help you through the process in the best way.

However, the correct procedure would be to unmap the LUNs from the app servers then split the mirrors. Then map linear volume back to the app server.

Make sure you split from the Datacore server you want to keep at the original location.

Then you can unpartner and it will not affect your data.

if you unpartner without first doing this, you stand a good chance of loosing both sides of the mirror.