I've dwelled on this myself, actually. My musings had led me to believe that the core of the fan base will exponentially diminish following the conclusion of the series. EqD will continue to post fan arts and updates on the cast/crew of MLP as they move onto other projects, but will slide away. The rest of the "fanbase" will follow, as DeviantART submissions for Pony Art slow to a crawl.
However, I do think that pockets of MLP fan communities will thrive. Dedicated groups that will continue to discuss the show, continue to do fan art, and continue to try and introduce others to the show for years to come. Tight-knit communities can survive long after their original "purpose" has become moot (indeed, oftentimes its a requirement, as the original topic for discussion might grow bland or saturated before it is concluded).
PonyGAF itself will most likely linger on in some form or another a year or so after the show wraps up. For how long and in what capacity I cannot say.
But in the meantime, thank goodness for top-notch art like this. This community really rocks.
