I'm a retired Clinical Social Worker, a grandmother and a foster mother to young (birth to age 8 when they come to me). I have found that there are somethings that you simply can't force and potty training is at the top of the list. It seems to me that since your James was trained before age two and only regressed after Daddy went away, the regression is primarily a control issue. His world changed drastically and he likely is frightened, feeling insecure, and feels his world has gone totally out of control. Going to the potty is one thing that he can control though. In my opinion the best way to handle it is to put the pull ups back on him and when you change him say things that reinforce that he is still a big boy and can control things. For example, You might say something like: Honey, you know you are my big boy. When you want to go the potty and wear your big boy underware again, you can tell me. Then we will get them out of .... and you can put them back on.
Other than that, I would ignore the problem but keep on telling him what a big boy he is, particularly when he does things of his of his independent volition....eg., help pick up the toys, help you put the clothes in the clothes dryer, etc. I bet it won't be long before he returns to the potty. It may not happen until your husband returns home, but there is a good chance it will happen sooner. At age two, children are just starting to realize that they are separate people from their parents and that they can control somethings.They are starting to like to "help" and while this may slow down the completion of the task, it helps the child develop the needed sense of control and to begin to develop a healthy sense of independence. If you have a rocking chair, hold and rocking is a wonderful way to help him regain his sense of security.
Be patient and good luck.
C. B