Okay, Homeric last first:
The Tarsai have escaped before by attacking cargo ships and forcing the pilots to take them off world. Since it takes a little while for the power drain to become apparent ships have been known to land there for repairs. Thats reason one. Reason two is simply that the Agamari cannot concieve of strategic defeat, tactical defeat yes, but no strategic.
You don't want to make an enemy of an Agamarian because he'll keep coming until he's dead and the rest of his family until your dead, and the rest of his clan until your family is dead.
You get the picture.
As far as stripping them of everything they rely on, well I did consider having a blanket "no" on magic which would have hit more of the group but there are still going to be problems, for instance comlinks won't work.
As far as the confiscation thing, well the group will have to pass through the Tol Dura fortress in order to head north and into the underworld. Added to this the first thing that will happen will be that the group will be attacked, as soon as the hatch opens. Since the Asgardried is a large ship it will attract a large force.
The group will be saved by Agamari cavalry which will have been sent out on seeing the ship enter the atmosphere.
At that point the group will be faced with (checks notes) 60 heavy Cav with lances and 120 fast horse archers. I'd like to see them get out of that, especially since the Agamarian leader was generous enough to send spare horses. Speaking of which what is the size of the group now?