Defunct Company Gear Value

It clearly depends on the company. . . although it may be different between electronics and speakers. Just look at the price of a pair of Rogers LS3/5a.

The aforementioned Dunlavy and Threshold might be a bit unique in that besides having technical and sonic prowess that still compete with more modern offerings, they also have some type of support available.
The Threshold gear still has support through Nelson Pass' recommended ex Threshold tech Jon Soderberg of vintageamprepair.net as well as advice from Mr. Pass himself on diyaudio.com.
The Dunlavy's used mostly off the shelf parts, that for the most part are still readily available.

Unsound, You are absolutely correct regarding Threshold values. Once folks became aware of Soderberg and Pass Labs started up Threshold values immediately started to climb. However, I believe Dunlavy speaker values are strictly based on performance.

Good example of prices dropping after a Co. goes out of business are the Hales speakers that I used to own...Paul Hales closes up shop and the next day the speakers dropped in value by at least 70%! Same for numerous cable manufacturers that have gone out of business. Highwire cables come to mind. Highwire closes up shop and "voila" values drop like a stone! Plus, the other issue is that now nobody has heard of the Company, leading to even more depreciation....IMHO, the moral of the story should be to buy ONLY gear from a larger well known vendor, IF you are concerned about re-sale value.

Hasmarto, a few thoughts, my perspective only.

The issue about warrenty is a straw dog. Most audio gear has no more than a one year warrenty anyway so that may have little affect on used values.

Overall brand reputation has a big influence. Case in point the Dunlavy speakers. But in that case the same brand of replacement drivers is not a complete answer. I'm not sure about DAL speakers but Duntech Audio utilized matched drivers - with one another when paired and as fine-tuned by the crossover. So simply replacing with the same part number might not insure original performance.

Then there is the question of the same designer/owner ending one brand and starting another. At least they might advise on any necessary repairs. The Threshold/Pass example is a good one. And what about Carver? He has had at least three companies; what has been the used values for his products?