We agree that you will probably not face future visa problems for having broken the contract in your first teaching position as your employer had hired you illegally. It will simply appear as if you had been in China as a tourist and that shouldn’t draw any suspicion.
We have included a detailed discussion about what is required to transition into careers other than teaching English in the Guide under Outside and Other Employment
(see, especially, Transitioning From English Teaching to Other Careers in China
Generally speaking, foreigners who are hired by international companies to work in China in fields other than teaching English were already working in those or similar positions back home. Western companies with branch offices in China typically recruit from their own domestic pool of employees, that is, staff already known to them who have proven they can do the job. In the absence of that specific employment background, experience in China and even Chinese language skills will not generally count for very much. Local companies in China that seek an unqualified foreigner to work in some capacity other than teaching English (as was the case with your former roommate) will typically pay that employee a salary comparable to what a Chinese national would earn.
Your best bet would be to try and find an entry level position in a company with a presence in China, and then eventually ask to transfer to China. As a rule, it is very difficult to build the qualifications you would need for such a position if you are already in China, i.e., hadn’t already met the educational and experience requirements prior to relocating.