The placing of the post is 'odd', you've asked for the opinion of 'pros' in the general section and therefore had only a few pros respond.
That said, you've probably realised now there are a lot of good reasons to have a second body. But for pro's it's a no-brainer, you can't just pack up and walk off a job because of equipment failure. It's often discussed with relation to weddings (purely because there are a lot of wedding photographers about). But I can't think of a single pro assignment where it'd be OK to just announce you'll have to come back at another date when you've had your camera fixed.
It ought to be obvious before you take your first step on the pro ladder, you need all the necessary knowledge, skills and gear.