All the characters that have departed from the show
I'm in the US and so I'm watching Saving Hope on Ion's schedule, meaning that I've just started season four. Now Melanda is missing from the season four premiere, having left in between seasons, acknowledged in just half a sentence that I didn't really even pick up on initially. Before that there was Joel in the season three finale, and Reycraft [3.7 was his last] and Gavin [3.4 was his last] before him. (And Gavin's successor, Dr. Dey, whose last episode was 3.18, for that matter.) That means that five characters (four regulars) left during, or at the end of, the third season, which seems like serious cast shrinkage.
It looks like some new doctors will be joining the team this season, but I miss the original crew. Still, six regulars (Alex, Charlie, Maggie, Zach, Shahir and Dawn) is a pretty large cast, especially for a Canadian show. Anyway, there are already threads about the individual character departures, but I wanted to mention the thinning out of the ranks ...
We know that Daniel Gillies wanted to leave the show due to time committments:
http://www.thetvjunkies.com/daniel-gillies-saving-hope-finale/
Not sure why the others left, whether it was their decision or the producers'.