An in-line load balancer in front of Expressway-E? Very funny but it isn’t April fools yet. This is not supported and I can imagine a litany of ways attempting it would go badly.
Cisco supports GeoDNS and/or multiple DNS SRV records (though Jabber doesn’t respect weights and priorities). There are multiple failover limitations in current versions and they are documented in the Preferred Architecture and/or MRA documents. Worst case is a user that needs to quit and relaunch Jabber to recover. Yes, there are plans to address/improve failover but I’m prohibited from sharing roadmap details on the forums since they require an NDA.