I can understand them not wanting to finish a job that was started, as sometimes people don't know what they are doing. The parts that were left were the easiest parts. It was just going to be too difficult for one person to do.
As for the paying some one to help, I usually trade work for work. I help with roofing their house, concrete work and so forth, they come and help me. This time they didn't show up left me in a vulnerable position with a partially bare roof.