Well a very strange thing happened to my poor ranger.
His companion just disappeared. I had him summoned, i told it to stand ground, while my char disposed of some crag cats, while the last one ran away, i chased it and the animal companion suddenly disappeared from the party.
In my combat log there was no mention of it dying, nor that it got unsummoned, or that it was fighting(no rolls, no damage etc.). It had full hp, then the next moment, it is not in my party.
Sadly about 3 minutes later my character died, and had to respawn. Mechanically the animal companion is treated dead, even though no message in the combat log stated it.(looked it through three times!) No damage was taken by the animal companion and i was at maximum 1.5 half screen away from it.
So from full hp it disappeared, and now is considered dead.