Hello Raul,
I don't think there is anything like HA for user agent.
For example, let's say you have HA in AD where 1 (active) AD would respond/generate logon/logoff logs and other be just standby.
You can add both of them to single user agent and then if one of the AD fails, other one would respond to user agent.
But there is no HA schema for user agent to be specific.
Hope this helps.
Rate if helps.
Yogesh