I don't think they're going to offer you anything at all. The letter that you were sent was merely a fact finding letter to see if you were still active and using your website. If you're not willing to give it up they'll simply register a similar domain name of their choosing (ie. concretebluesjeans.com, cbjeans.com, cbj.com, etc.). They have zero brand recognition right now so they can start with whatever they want. They're not tied down to any specific domain name.
For example, our company sells a line of vehicle lubrication equipment from a manufacturer named Graco. Mostly unheard of to the general public. There is also a company called Graco that sells baby gear (strollers, car seats, etc). I'm sure many of you know of them (I know I do!). Well Graco the lube company got graco.com first. What did the baby gear company do? They registered gracobaby.com. Done deal and it didn't cost them a penny. And people are still able to find their website with no problem.
I think once they find out that you are still using your domain name, they'll just move on to their second choice. In the end I think you'll be better off if that happens. In the off chance that this company makes it big, you'll get all sorts of random hits to your site from people searching for the other company.
This is a viable point of view as well.....
What it boils down to is they haven't offered anything yet either way. So OP needs to email them back, professionally, and tell them that the site is in fact, active. And not say much else. See where the chips land.
