Defunct Company Gear Value

For the most part Larryi is correct, the prices will initally drop dramatically. As J.D. points out with Dunlavy though, some will hold their value remarkably well.
Threshold is another example of a company that went out of business that's products hold remarkable value, even the Forte line.

Threshold and Dunlavy are not the norm though.

Rgrog, I did say that prices drop dramatically initailly, for any company that goes out of business. However, some do recover. There is a pair of Threshold SA-1 monoblocks on Audiogon now for $4750, that comes to 79% of their original $6000 list price. I think that's holding value pretty well for a pair of 25 year old monoblocks.
I know not all Threshold's still sell for 79% of list, but they seem to do very well on the used market compared to other defunct companies. They even have their own website, Thresholdlovers.com, not many can say that either.

FWIW, you can get good deals this way. I'm currently enjoying a pair of Soliloquy 6.3i's that I paid less than 22% of list for. I thought they were a very good value at their original price, even better at 78% discount.

Rrog, I got the $6000 list price from a 1986 Stereophile review. Perhaps the price went up and was $8500 when the model was discontinued. Still, even 37% is pretty good for a 20+ year old amp from a company that no longer exist. I paid around 22% for a 19 year old amp from a company that still does exist.