Auto Balanced Collector Group vs Failover?

As far as I know, ABCG isn't that intelligent. nor does it mention along those lines at https://www.logicmonitor.com/support/collectors/collector-groups/auto-balanced-collector-groups. I wouldn't suggest doing ABCG across sites.

Note, you may want to be careful about even normal fail-over to a different site. If a site goes down due to internet or power, all the devices would switch over the other site's collector. Since that collector is live but can't reach all those devices, it's going to alert on each and every device at that site as being down. I believe the Dependent Alert Mapping may help prevent that issue though.