Ok, here's my take on things at the moment:
- we just saw something big take out our own big guy, which is cause for alarm (especially since Mag has seen Agnak in battle and knows what he's capable of)
- now there's another big thing that looks like it wants to fight the first thing, and under the circumstances we have no reason to assume it's friendly
- we're invisible and (presumably) haven't been noticed
The most logical thing would be to let the two duke it out, then attack the survivor after it's been weakened. The only reason I/Mag would consider rushing in is if we thought Agnak was still alive.