DL = Dean's List
Not placing high in the class rank does not necessarily correlate to not getting a placement through the recruitment processes. I know of colleagues with GPAs not even within the top 50% who got placements and individuals with higher grades who did not. It really comes down to a mix of your interviewing skills, networking and sheer luck.
Putting that aside, regarding what happens if you do not get a placement through the recruitment processes, I think most of our class ends up somewhere by the time articling comes around. Whether or not its their first choice is hard to tell. The CDO is still working on building the data to be able to give us numbers. However, I haven't heard of it being a problem...
Edit: also, if you look through the course aux stage thread in civil schools on this website you can get a sense of average GPAs that individuals who get interviews from McGill have.