I wouldn't think the value would change now vs when they were "active. The Heads wont function any better/worse now. Its not like others can't support repairing/rebuilding them if required. Just no new products to follow.
On that note as well..it saddens me when I see these company's closing for this reason (no apparent predecessor) or someone to buy and continue the product line. In this instance there are others making a similar product with a diminishing market. Great product none the less...again my