If my iPad is lost, how do I know when it has been removed from my Apple ID account?

I lost my son's iPad this afternoon. By the time I realized I couldn't find it and pulled out my phone to use the Find Phone My iPhone app, it may have been too late to set it up as lost. The iPad is still displaying in the app, but simply as offline. Of course, the iPad could be laying on the street somewhere, God only knows. However, if someone had reset the iPad and logged it into their own account, would it still display on my "Find My iPhone" account even if it were offline? Or, since they can reset it without being online, will it wait to refresh until they get it online? I am literally sick to my stomach, I just bought this 64 gig brand new mini two months ago for my autistic son, and he uses it daily. I cannot fathom the idea that it is not in the house, but if it were in the house, it would be connected to our Wifi automatically, and it would not be dead because I just charged it for him for our short trip today. How can I see if the seriel number is even still on my account? When I go into my account, it shows a white mini ipad, ours is black, and it does not show the same seriel number. HOWEVER, it does show that I called about the Mini on the 29th of October, so even though it is displaying as white with a randomly different seriel number, I did call about an issue on that device. Why would iTunes have a different mini seriel number set up under our account? If you cannot tell, I am freaking out. We're out $500 and I feel like there just has to be a way to get our iPad back. (Just for all of you KARMA beleivers out there: About a year and a few months ago, I was at the pool with my son and found a Kindle Fire. I immediately went through to find the owners information and contacted her to return it! There has to be good Karma for me in this situation!! ;-) ) Please, help me determine if the iPad is still connected to my account! Anything! Thanks!