I think it would be best for him to take the time necessary to heal and to rebuilt strength in the knee and legs. I don't have to tell him that because he has been through it. If the Cowboys have another year like this year, they won't really need him to come back. The season will be over by Thanksgiving and he can take his time rehabbing.
For those saying he will never play again, I think that is overly pessimistic. Sports medicine is not the same as it was even 10 years ago. They can do so much more with injuries like his now. He'll be back but it may take more time than he thinks to get there.