I think the best thing to do is focus on training, but pick your fights. If you know you can't win a game, then just train. If you are certain you have a chance (let's face it, 3 other teams promoted with you) then go for the win. Try to aim for 5th-7th. TIE for games you'll lose for sure, and CT/Normal for games you have a shot at winning.
I trained my SF trainee at PG for a whole season whilst I was in Div II, and I got relegated. I initially thought about tanking, but changed my mind and made a late run, but it was too late. He was a C at the time, and needed lots of work. Although I don't regret the training, going back down to Div III hurt me really bad, and I was lucky to make it back up because my main rival from the other conference got knocked out early in the playoffs.
Things to remember:
- What you used to make in your old division per week will drop significantly once you're relegated.
- You might end up in a hard division with another team with a squad better than you, so you might get stuck in the lower division for more than one season.
I think you'll feel much better if you manage to maintain a good training program and stay in the same division, rather than copping out and just giving up on the season.