A scaling back of the budgets may occur regardless of the box office performance of DOFP. Using the quick & dirty "profit equals double the WW box office" method, the three most profitable X films were those with the three lowest budgets - X-Men, X-2 and The Wolverine. Using that method, DOFP will have to bring in close to $600 million in order to generate as much profit from ticket sales than the first movie in the series.
Though it may upset some fans, it may make sense for FOX to fill in the modest budget niche that Marvel, Warner Brothers and Sony appear to have abandoned. Though Apolcalypse would be tough to pull off on a "The Wolverine" budget, FOX could move forward with a Wolverine sequel, Deadpool, X-Force and other spinoffs (Mystique spy thriller?) without being dependent on the mega grosses that the other studios are chasing.