First of all, this sort of reminds me of copyrighted logo reproduction. These plans were originally created by someone for your customers, they should be able to go back to their source and get what they need, or else they don't have the right to it. I mean if I was working with an architect and I wanted a workable copy of the plans, I go back to my architect and get them, not go to some vectorizing guy.
I agree in concept but had a project that makes me see why a backup plan is necessary.
A couple of years ago, we had an order to print emergency evacuation maps to go on the back of doors inside of hotel rooms. The hotel is 30 years old and all they had were very grainy black and white copies of the floor plans to work from. No architect name in sight.
In this case, there is no choice but to redraw the maps.