Like what exactly? I can't think of a single show that ended and still kept 3/4th of its community.
The first one that comes to mind is Firefly. It was cancelled due to lack of viewers before it finished a single season, but a few years later, had retained enough fans, and attracted enough new fans to justify making a full length film, comics, and an RPG.
Cancelled shows never completely die. Fans don't just go "ok shows cancelled, time to completely stop caring"
Yes, a decent amount of people who just watch the show will forget about it eventually, but some of the more "hardcore bronies" whose actions range from creating custom pony characters, to spending thousands of dollars on costumes, are not going to.