It depends on what Wests want to happen really. When Wests took over there was a lot of posts about how they will expect success from the club, and demand it.
So if Brown isn't measuring up to whatever yardstick they have for his tenure he will go. Considering they only just signed him to an open ended agreement, stating they wanted Brown at the club for the long term, I can't see them knee jerk sacking him based on not achieving a certain place.
A lot will depend on injuries. If we get another year of key injuries like last year that will have to be factored in.
Top 8 is pass, anything else is fail, Browns tenure is up to Wests beyond that.