the cat is very easy to save. don't go near guards with a cat.
I can even tell you 2 simple ways to save it without any mods.
1)if you're playing solo - take a route through the ladder (the cat will wait there) without encountering dallis.
kill everything inside the fort and then either kill dallis or trigger the encounter normally.
get back your cat and escape through the bridge
2)if you're playing with a party in single player (or in multiplayer in a party of 3 or less real players). select a character who is followed by a cat and leave him in a safe place. statue of braccus rex will do. alternatively select an npc you don't need and talk to the cat. without ending the dialogue switch to the other characters and play normally. then kill everything and proceed like in a var 1.
