Metro Ethernet network with redundant internet connectivity at two of the four sites - Flow Redirect?

We are currently exploring implementing a backup internet connection at our DR (or COB if you prefer) facility to serve internet connectivity for all sites in the event that the primary internet connection is lost, or all remaining networks in the event that the primary site is completely down. Routes are currently static, transitioning to RIPv2 soon. Is Flow-Redirect the best method for determining if the internet is in service at Site A (and if Site A is in service) from the core switches at the other 4 sites or is there another feature better suited for this function? For reference see brief rundown of network below.

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Site A - Primary datacenter / primary internet connection - 4 VLANs

Site B - Branch facility - 3 VLANs

Site C - Branch facility - 3 VLANs

Site D - Continuity of Business datacenter (replicas of all VMs with varying RPOs, LOB databases at 15 minute RPO) / branch facility - 6 VLANS

Replication occurs between the two vCenters as well as between 2 SANs. Log shipping is implemented for the LOB databases.

Devices are X460G2 (core switches) and X450G2 at edge where necessary.

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Thanks for your input