I’ve found it pretty straightforward in this last patch as long as you break into the room from the raised walkway from the building next door while in turn based mode and keep the character you want to go in far enough back not to be knocked down by the blast when the door breaks. The pathing isn’t perfect, but at least he’ll actually get up now and run through the door you broke down to get to him (though you might need to get out his way) rather than lying there which he did previously.
But I’m sure that the first time I did this quest I did manage to rescue him after breaking in from the inn itself, and that did seem to become (nearly?) impossible in a later patch. I confess I’ve not even tried to do this for ages as it was so frustrating.
And none of this takes away from the fact that the design of this encounter absolutely needs changing to be less annoying and require less meta gaming to complete successfully. At the very least, the game should automatically put you in turn based mode when the door opens, in the same way as it does for traps that require time-sensitive action to escape (eg the trapped tomb in the ruins).
