Why the need or want for a second body? Personally I've survived 15 years of not having a second body and none either film 35 or MF or digi FF have let me down. - I have and several lenses let me down tho, in which case id just adapt and use another one.
anyone who gets paid to shoot a wedding should absolutely have a 2nd body on them. even if its a rebel. you would be crazy not to and certainly tempting fate.
i had a shutter explode on me while i was shooting getting ready shots. it was my only camera. thank god i was the 2nd shooter and the main shooter was able to toss me her spare 3rd body. could you imagine if i was on my own! after that i immediately got a 2nd camera.
now i carry 3 bodies with me. 2 for shooting and the 3rd for end of the world nightmare scenario backup. and i always have a 2nd shooter with me.
ive been shooting professionally for 15 years now on my own and with about a dozen other photographers over the years. every single one of them carried 2 and sometimes 3 bodies with them on shoots. regardless of what kind of job it was. during that time i have seen cameras die in a variety of ways...more than i care to recall.
part of being a professional means you can get the job done no matter what. not having a back up camera is inexcusable under paid circumstances.
oh...and to the OP, get another 5d3 if you can. why not?