Where did you hear that many students who do well may not get a residency? Have ya looked this years and past years match list?
I did not take a LOA but know of people who have had personal issues to deal with and took a LOA. That said, the only downside is that you will be graduating with your current class but in the next years class. If you keep the GPA up as high as possible once you come back from the LOA, and do everything else you need to in order to graduate, you should be able to match.
Also, read your students handbook and talk to admins..don't listen to rumors from people who may not wth they are talking about.