Not all worker co-ops work out well. I worked at one, Westat, and it treated people absolutely as badly as other places I (and coworkers) have worked.
I agree. There will be worker coops that fail and go out of business (just as happens to capitalist enterprises) although I would expect that a worker-coop based economy would have cooperative ways to support coop-workers who lose jobs and need help in relocating to other coop jobs etc. Nor are worker coops guaranteed to behave as we want in all cases. Indeed, all sorts of bad habits etc will survive for a while in an economy transitioning from capitalist to worker-coop enterprises; these can and will show up again inside the new worker coop enterprises. Those of us who favor worker coops as a better economic foundation for a democratic society will always need to be vigilant that worker coops do in fact contribute to the larger good society that motivates our support for worker coops in the first place.