Unfortunately, that's not possible. When you leave a project, it gets abandoned. If someone else already was in this project, you can ask this person to invite you to it.
Well unfortunately that person had not yet accepted the project invite. I've lost two hours of work. That a really really bad design David. The "leave this project" button is a huge trap for new users. You must change this. I think I'll consider another app since I can't afford for this to happen again somewhere else in the tool -- and no back ups except for premium users -- really? You can't base a cloud app on that premise.