You need to look into volume licensing.
Casper can deploy Office for Mac and its updates but it cannot perform the online activation Office 365 requires. That licensing information is not stored on the computer but rather the computer periodically checks that it's still allowed to run the software.
I suggest you keep your old licenses because they are valid in perpetuity. Office 365 licenses expire annually and you must renew all your Macs each year. Again, look into volume licensing. Volume license versions of Office for Mac work with Office 365 services.
Hope this helps!