Oh that's a good theory and would explain it well!!
Now, IF Snape is still working for the OOTP, who is he reporting to with D dead (or everyone thinking he is)? Is McGonagall in on it? Is he going to report to anyone at all or is he a deep agent put in place to be ready at the final battle?
I think that Snape is working on his own now, independent of the other Order members. They all seemed genuinely shocked at Snape's actions. McGonagall is in the Order, but if Hogwarts openes in the next book, she'll be Headmistress. That will give Harry access to DD's portrait, even if he doesn't return to school. I'm interested in seeing what becomes of his education--I don't think he's through at Hogwarts. I can't see him leaving Ron and Hermione, and if the school reopens, they will definitely attend.