Whether or not you can save it would depend on how long it's been in bone dry soil. If the roots aren't dead, keeping it moist - NOT soggy - should revive it. It's going to be in the 70's every day this week, so you could keep it outside all week - I only bring my tropical passis into my house when the nighttime temps go below 40 degrees, which has only happened twice so far this year, no freeze yet. Even if you don't see any top growth this year, don't give up on it - you may very well see new growth next spring.
Sherry

Should I just prune all this old growth?

I would prune it back give it a healthy shot of Super Thrive put it in the shade outside for as long as you can.. Don't keep it to wet.. If the root system is good you should be alright.. there are several that are hardy where you live did they give you any kind of name for it??
BTW!!! Congrats... and Welcome!!!
Chena

Thanks Chena, I'll do just that. The tag says Passiflora x alatocaerulea

Okay.. I'm not sure how far South you are...I would probablly bring it in since it has been stressed and give it a chance...BUT is your are way South...LOL where are ya???
Chena

Here is a link that might be useful: Passi

Chena, I am in Houma. Once you go lower than Houma other than the barrier islands, you are in the Gulf. My hubby does oil exploration out here.

I think it says Z9 .. is that you??? You could plant it and leave it out ...LOL How cool would that be..

Don't give up on it even if it doesn't grow for a looooong time- I've had passi's who appeared dead from frost or lack of water or whatever even to the point where the top completely died. I put the pot somewhere thinking I'd eventually recycle the dirt only to find little sprouts coming up from the roots in the spring. 'Course by then I'd lost the tag & had no idea what it was...

I planted a p. incarnata in an overly shady spot about ?9 years ago, and it never did anything, then finally quit coming up at all - I forgot all about it. This past spring I noticed a sprig of it coming up, I scratched my head, dug it up, transplanted it to a sunny site at the bottom of my new fence, mixed chicken manure into the new planting mixture, and it proceeded to spread like a weed all over the fence! Of course, it got eaten to the nubs by gulf frit caterpillars, but it looks like I've got a good vine that'll make the usual wide spreading colony - those passies are amazing!
Sherry