What Happens To Old Software?

whatsit asks: "I was recently reminded of a little DOS database called Nutplus (also called Nutshell in its earlier versions) and decided to contact the company that owned it in hopes that they would open source it. After some research and some tears, I found that they may be out of business! I found a Web site address: www.fairsoft.com that doesn't work. The company's name is/was Fairhaven Software. I also came across an 800 number and a long distance number for them, but both ring busy. What happens to old software when the company that owns it goes out of business? How can I go about getting rights to the source code? Does anyone have experience with a similar situation? Do copyrights on these pieces of software ever expire?" Are there any ways to obtain the rights to software after the parent company is long gone (assuming the code happens to exist after the lifespan of said company)?