I'm sorry but its completely ridiculous to suggest the death or decline of any sport just because a champion retires. The reasons for Indycar's decline (or more accurately, toeing the fine line) are everything to do with the management of the sport and its struggles to find its place competing against NASCAR and F1.
It should be pointed that Franchitti was hardly a young driver with a big career ahead of him, he wasn't a superstar that everyone tuned into watch and he wasn't going to turn a load of heads if he had switched to NASCAR, F1 or WEC. He has his supporters sure, just like any successful driver, but to suggest he somehow defines Indycar is quite ludicrous.
Nothing wrong with you deciding not to watch any more, but don't go suggesting everyone feels the same way.
Not being able to name many Indycar drivers is less of a compliment to Franchitti (he gets the odd bit of coverage in the UK press) and more to do with the relative poor status of Indycar.
I wouldn't be surprised if people couldn't name any Indycar drivers nevermind Franchitti. Anyone from the UK would name Franchitti simply because he gets the odd bit of press due to his nationality - not because he is the biggest name in the sport.
I would have argued Rubens Barrichello was a bigger name last year. I'm sure a lot of Americans will disagree with you about naming US open wheel drivers.
I hate to say this in a thread that should really about applauding the end of a great career but well, it needs to be said. There is no need to exaggerate and inflate Franchitti's achievements.