Finally had a reply from Cisco Meraki - thought I would share:
Thank you for contacting Cisco Meraki Support.
They way the Meraki dashboard is set up is that the MDM functions will cease functions also when the grace period has expired.
What we can do is once the licensing does expire in 74 days, we can remove the AP licenses and it will allow the use of the MDM functions. We need to wait until the keys have expired and the devices are removed from the dashboard before removing the key.
When the keys do expire, please contact us again and reference this case and we can remove the keys. Once the keys expire there is a 30 day grace period, so the MDM functions will not be affected.
So, in short - yes the MDM will still work, but there are some changes to be made to the dashboard first.
