I don't see Dubnyk getting the type of offer you outlined. If Dubnyk plays basically at the same level as last year $4m aav on a 3 year term is what a reasonable offer would be.
I just don't see the team even bothering to keep him around if he doesn't take a big step forward next year.
I wouldn't say he let in a weak goal every game in the first period. Sometimes he saved the softies for the second or third period.
Given how he played and considering the support he had when Smid and Petry were not on the ice, I think he's good for 4M per season. Even if his play vastly improves next year and he is no longer prone to giving up a weak goal every game I couldn't see him get more than a 3 year deal unless we go to the playoffs next season and he shows a lot of promise.