Is there any way to rehab an abused down sleeping bag?

You could try the cleaning suggestions shown here which claims that:  “The result is unbelievable: the bag will look like fresh from the store, in full volume and ready for the mountains!”

http://patagoniandreams.com/2011/10/16/gear-do-it-yourself-how-to-clean-a-down-sleeping-bag/

Well, yes. Loft, with good down, can be restored just by washing. Warm water (not hot) will help to fluff any down. Try not to disturb it too much in the mean time. The tangled clusters can tear at each other. And, good down is relatively fragile.

Heat, up to steam heat, does not hurt the down feathers, but CAN ruin the modern synthetics: shell, zippers, cords and velcro. I note this because it is not so much the down that gets hurt, but the shell.

Simply washing it with down wash and drying it in a warm dryer will help immensely. Use plenty of soap to restore loft. Soap tends to make the wash water slippery and will lube the process of disentangling the down. Dryer balls, tennis balls, etc can be used to beat out any clumps. But, do not use heavy items, sneakers for example. These can cause damage to the down & seams; simply too heavy.

Most down compression damage can be traced to entanglement of the down causing fibers to rip apart, and, bent fibers within the down. Good down (>700fp) is mostly powder down, not the stalky down in cheaper lower lofting down fills. But, there is usually some. Bending these stalks can be bad, these are often permanently kinked. There is no way to repair that.

Storing down damp & compressed can create a permanent problem. Molds, fungi, bacteria, and bugs can destroy down. The acids from these critters can eat away at down (some bugs will actually eat the down) leaving nothing but powder. If it was dry when stored in the bag, it is likely fine.

I would simply start with a good washing.

Hey Thanks.  I’ll give it a shot!

If washing doesn’t help enough. I’ve heard of people undoing the switching and stuffing their bag with new down. It’s alot of work but a hell of a lot cheaper than $600

If you use a washing machine, I would suggest you run a hot cycle first without any clothes or detergents.
The idea is to wash out some of the detergent remains from it.
(and yes use pure soap/down soap not detergent for the bag…)
Rinse well.

+1 to Franco’s suggestion.  I always do the above before washing any Down product.