It would be the end of TNA as we know it for sure because we know TNA with Kurt Angle in it. Any further extent of Kurt Angle leaving would not be too great I would assume. As people have mentioned previously, TNA was doing just fine on it's own, before Kurt even came to TNA. Sure, Kurt Angle gave TNA a level of viewership that it had not seen before and might not see again. However, TNA know that Kurt Angle and Sting are not going to around forever and will surely have contingency plans for when they leave. For example, WWE know that Shawn Micheals and The Undertaker are not going to be around for a lot longer anyway and as such have tried to elavate others in their stead. I think that when Kurt does eventually leave TNA, the viewership might suffer for a while but TNA will continue to go on without him. At the end of the day they are planning for the future all the time and to not have any sort of plan B is liabilty on their part.