They disappear when you destroy the bots because that's how the event works. This is described in the details screen of the event.
When he reaches 30 stacks of the Rage (not hatred) in the event he will become enraged. I am not sure on the specific gains for enrage in that event, but he becomes unbeatable and has a bunch of offense to kill a toon each attack.
Dark Rage and Malak's Hatred are two different things. Malak's Hatred is a blue mechanic placed on Revan on both sides of the event, and says it gives Malak's attacks additional effects against him. Don't think I've ever read what those are though.
Edit: the effects are listed in Malak's abilities:
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When he reaches 30 stacks of the Rage (not hatred) in the event he will become enraged. I am not sure on the specific gains for enrage in that event, but he becomes unbeatable and has a bunch of offense to kill a toon each attack.
I was confused by this line:
All Dark Rage is, is a counter you need to keep below 30 to avoid enrage. That's it.
Edit: the effects are listed in Malak's abilities: