The NWA has the longest title liniage of any championship belt out there (though it be scwed in contraversy over different situations)
The National Wrestling Association (not the NWA we now know) started in 1903. The National Wrestling Alliance (which is the NWA we all know now), started in like the 40's or 50's.
Somewhere near the beginging of the Allaince, they had a unifaction match. The original NWA folded shortly after.
World Championship Wrestling became part of the NWA, and although they did have there own WCW Championship, they also had the NWA Championship. Unlike the agreement with TNA the NWA titles were not exclusive to WCW, but WCW did have control of them. (why the belt never got dropped to a none WCW wrestler.)
In 1991, Ric Flair left WCW and was the current NWA World Heavyweight Champion. When NWA refused to repay his deposit on the belt, Flair sent the belt to the WWE where Bobby Heenan holding the NWA Title on WWE's weekly TV declared "The REAL World Champion is coming to the WWF" (WWE's name at the time) Flair arrived and after lawsuits and what not the NWA title was returned to the NWA who crownd a new champion. Flair was officially stripped of the championship.
Another skew in the liniage happened when the NWA and WCW severed all ties with eachother. But because WCW had paid the fee to Flair to get the belt back in the above incedent they kept the belt, and the NWA went back to there traditional design that you know now. The NWA Title was renamed in WCW the Internationl Title which was currently held by Rick Rude and fueded with Ric Flair who was now back in WCW. Eventually I beleive Sting won the International Title while Ric Flair won the WCW Title. Flair and Sting unified the belts with Flair going over, and the WCW Title belt was scrapped in favour of the big Gold Belt that was the NWA Title then International Title and was now the WCW Title belt.
When WCW was bought by WWE, the WCW title was defended and changed hands up to The Rock when WCW was droped the WCW Title was renamed the World Heavyweight Championship. Rock lost the title to Jericho in the Unification tournement in 2001, and Jericho then went on to beat Austin to win the WWE Title as well to become the Undisputed Champion. In the summer of 2002 the belts we reseperated as they are currently. Therefore in many ways the World Heavyweight Title that Batista holds is the original NWA liniage.
Other problems with the NWA title....Eastern Championship Wrestling became part of the National Wrestling Alliance, much like TNA has done now. Todd Gordon the creator of ECW & his buisness partner Paul Heyman, decided to sever ties with the NWA and go in there own direction changing the company to Extreme Championship Wrestling and Shane Douglas won the NWA Title in which he then threw down the title and declared himself the new/first ECW Champion. Again the NWA took back there belt and crownd a new champion.
When TNA started they made a deal for the NWA Titles, as mentioned its a limited deal and was used to help jump start TNA with a ligit wrestling history. Sadly as you the man who started this post, are not really aware of this history and therefore don't care. This is why as someone else said most likely TNA assuming they are still a stable company will most likely not renew there ties with the NWA as the majority of most tv watching fans don't know and/or care about the NWA histoy.
(I know some of my details are not accurate but there as close as I remember)