Quote from totalanime
The manga won't end until the end of their 3rd year, I think. the question is, how slow is the manga going to move?
well at this point we can't really know what the mangaka is planning. I mean over 250 chapters and it is still the second year... and I am getting th feeling that the manga has been putting alot of emphasis over the ending of the second year. Also, as it stands Karasuma is gonna leave at the end of secon year. If that happens that will mess up a major plotline in the school rumble universe. It all comes down to what the mangaka is planning on doing. Personally I would love to see a 3rd year school rumble cast and who knows maybe the mangaka can delay karasuma's leaving and draw in a love rival for tenma combating for karasuma's affection... Also, maybe a new female love interest for Harima that is aggresive in her attempts (someting like Satsuki from Ichigo 100%) which might lead to even more misunderstandings and maybe make Eri Sawachika jealous and take action.
I know I got a little carried away, the point is that there is still alot that the mangaka can do with the story and I just hope that the plot gets revived somewhat if he decides to take this to year 3.