I booked with Airtours in May 2007 to go to Turkey summer 2008. Airtours have been trading for many many years selling cheap package holidays. By the time I travelled last July my booking had been taken over by Thomas Cook, wasn't a problem really, I still got the flight/hotel/holiday I booked, just a change of name. I think I had one hiccup over the paperwork caused by the changeover, although perhaps I was lucky. I failed to get an invoice showing that I had paid my final balance. I gave up asking and it turned up a day before my tickets. Might have had a flight time change as well, but I get these all the time if I book a year in advance.
Still not sure if the two company's merged of if it was a Thomas Cook takeover, I assume the later.
I wouldn't worry though, its not like you have booked with one of the companys that offer dynamic packages. You have booked a package holiday so you will be covered by the Package Holiday regulations for what that is worth.
I assume you are worrying because of the Freedom Direct/Hays travel fiasco. IMHO I don't think the Airtours/Thomas Cook thing is the same. If companys like Thomas Cook start failing then the whole Industry will be in turmoil.