Not really. The party has come to the attention of the cultists in Middenhiem. Mortus would be in more danger with them than she would be alone.
If the cultist are on to Mortus, Heinrich, Julian, Klaus, Ragni, Max, and Admund, it does not make sense to split away. You don't have a low profile, and you wouldn't be hard to find. And IF you are found and you're alone, now you're really defenseless. If some cultists jump us in an alley, this party is bristling with more guns, axes, and swords than the Knights Panther. Klaus alone counts as a handgunners detachment.