Thanks for reviving this thread. In most cases, while both MXs are up - primary should be active. while primary is down and warm spare is up - warm spare should be active. The availability status of the devices is available via getOrganizationDevicesAvailabilities. However, as pointed out, a split brain status is not available via API currently. There is an feature request for it, and if you can contact your Cisco account team - ask them to promote "MXIDEA-I-511". They'd know what to do.
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