Here is a post on a FC2 blog from Japan:
Its a shot of the original K-ON!! 4-koma (cell) manga, produced by Kakifly. As most of you probably know K-ON!! animation is based entirely upon these 4-koma.
Now, the bottom line says:
And finally, the next volume will be the final [volume]!
This one’s (presumably) an inner cover of one of the volumes sold in stores.
The three characters in the box by Azusa says “Final Volume/Iteration”.
So it looks like K-ON!! is finally ending. True enough, the 4-koma written by Kakifly already has Yui, Mio and Mugi entering university, so without the three it would be impossible to keep the HTT going. Even if it was possible it won’t have anything common with K-ON!! other than Azusa.
All good things must come to an end anyway.