Hi @Dannygere
I am not aware of a best practice document from Meraki on De-Establishing HA.
I believe you may disable HA from Appliance Status page (The sessions established on VIP will be disconnected) and remove the device from the network.
However Aaron published a well written document on the functionality of Warm Spare in Meraki.(Worth reading)
https://www.willette.works/mx-warm-spare/
Regards,
Ajit
AjitsNW@gmail.com
www.ajit.network