One of my good friends I met was because of this fandom. He needed someone to look at his fan fiction. I agreed. The most glorious friendship ever followed. All because of ponies. That's what made me want to give the fandom a second chance, and ultimately, a third and final chance. It was successful and I finished S1 E11 - S2 E3 within two or three days. This has brought a multitude of other friends that changed my life. I love (most of) the fandom and especially love to the show. This show is the ultimate stress relief. Even when the last fan of the show throws in the towel, I will still be watching. Didn't stop me on KnD won't stop me now.
The fandom will eventually die out if the show stops or it succumbs to the Spongebob effect. Although seeing how bronies buy a lot of the merch, I'm sure that Hasbro will try to keep its secondary fanbase happy.
I have to agree with several others, and believe that the fandom will eventually degrade over time, especially if the show is drastically changed (rebooted), or disappears altogether. What gives me hope on the other hand is one of Hasbro's other long running series, Transformers. I see plenty of people who are still into Transformers years after the original show came out, and those people are certainly out of the target demographic just like many of us are for MLP. I think if Hasbro respects what has made MLP so popular, and successful in recent years, then it'll be much easier for fans to stick around. Even if they decide to move on though, I feel there will still be some people who will never forget the good times this series has given them, and will help it live on through artwork, stories, and music as well. We won't be forgotten quickly, I'm sure of that much. I'll certainly never forget. It's a fad with potential longevity, if that makes sense.