lol they will not take any of what you left like the .net nor the .org. they will create another that really differs to what you have because they will consider how much traffic you'll get..lol so don't worry.
Yeah they will contact you (always have a contact page on your site). When they do, if the site is bringing you money, offer a deal: you maintain the site with information and advertisement and get a commission of the sales it makes. Like you working for them. If they don't agree, just tell them you'll give up ownership of the domain (NOT the site's content which you wrote, you can publish it on another site). Most of times they'll agree to either of the above, as it's too costly to go after some individual (unless you're a millionaire?)
So you have bought a domain but your not prepared to tell anyone who it is even though it's getting over 6k hits? Ok...
If the domain uses regular words, no way they will win if they threaten you. If it's like "lynyrdskynyrdrockstheusa" then you might have problems with the fanciful words.