Another vote for keeping kitty in his home - I think your instincts are dead on when you worry that taking him out of his home would be even more traumatizing. I totally understand your worry, though -- my two are so sweet, but a touch co-dependent. I usually worry a lot when we have to go out of town. My one cat will throw a crying fit when he thinks I've disappeared on him and left the house, when all I did was go off to take a shower.
(Haha, he's not the brightest...)
Maybe you can encourage your dad to hang around - read something, watch some TV, etc - so that your cat has some people time? Also, have you used a Feliway plug-in with your cat before? I've used it for stressful situations before (moving, having contractors in the house) and maybe it's my imagination, but it really does seem to help calm them down a bit...