It is difficult to say who will come out ahead (assuming Cons lose power and coalition forms the government). I can see scenarios where Cons could return with a majority at next election, I can also see scenario where Liberals (or Lib – NDP coalition) return with a majority next election.
It will all depend upon how well the coalition governs, what happens to the economy during the coalition government etc. The fate of coalition partners will depend upon how well the govern. If they do a terrible job of governing or fall apart in a few months, all three coalition partners will be diminished.
However, one thing is clear. If Conservative government falls, Harper is history, he is gone as the leader of Cons, they will pick a new leader. That of course will be a big unknown. If they pick a leader in the mold of Stockwell Day, we are looking at Liberal majority next time around. On the other hand, if they pick a red Tory (especially from Ontario or Maritimes), he will give Liberals a good fight in Ontario and Cons may well get a majority.
There are just too many unknowns to speculate who will benefit form the coalition government.