Yo, Ben, it doesn't happen all that often, getting my old down bags wet, but it has happened. I was remembering when it did, as in the past fourty-five years or so. It's really a long night when your down sleeper gets wet.
I started out camping with an Army surplus feathered bag as a young boy, brother, were those things crude, then moved into down, then poloargaurd, now, something else. I'd have to look at the lable to say what it is but I know it's one of the newer synthetics. I used to live in San Diego and moved to Utah about twenty years ago, so I know how dry it can be there, but I also know how rainy it can get along the coast and in the mountains. I was in the mountains a-lot in my teens thru my forties. Accidents did happen, like leaking water bottles, or a storm that snuck up on me without any waterproof wrappings; camping in a low spot; Or my Gortex stuff bag that got water in at the little cinch opening. Bummer. These things do happen.
I am carrying a little more weight with that synthetic bag, it is true, but I feel a lot safer with it. I have only been hyperthermic once, out there, but it was scarry and a near miss. It sneaks up on you so fast and then you are in real trouble. I am just going with my own experience, here.
As far as drying them out, wet down, it takes a very long time. I have done it over the fire, but it took like two days. I had to continually hold it up near the radiant heat, but not too close and rotate it, and continually fluff it up. It was a major hassel. And then for two days after that experience I had to lay it out on some rocks when ever I took a break. If you cannot dry it on the trail and you donot have enough warm dry clothes, and weather is moving in, I would leave the trail or FIND a way to dry it. A fire is your best bet.
A dryer works great but I don't know if it damages the down or not, but if you are in the woods, dryers are not too handy. I have noticed that commercial drying machines say not to dry down in them. I don't know if that is for the bennifit of their machines or the down garments.
You can use a down bag just fine, out on the trail, for as long a period as you want, you just have to care for it and be careful. Take precautions to keep it moisture free. I used to use a vapor barrior liner, but hated the clamy feel of it. Down bags are great cozy things, but too easy to get wet. If you have one and it is working out for you, keep it and have fun with it. It will serve you well.
Cost of down bags, these days, for me, are too great for my budget so I will stick with synthetic.
Best to ya.