I don't think Tesla will reduce Model S output but instead increase total production as much as possible, perhaps breaking 20k cars / Q1 2016, and continue increasing production, top estimates for Q4 2015 were 18k cars for the quarter, can't Tesla make 20k / 22k / 24k / 26k for the 2016 quarters ? BTW that would be 92k cars for 2016 ! The big question is does Tesla need to make any shutdowns in 2016. If that's possible and 50% of production is MX, that's 46k MX !
Tesla must do everything it can to achieve at least break even for 2016, so production must increase as much as possible. If production continues to increase in a solid pace.
Just for quicks, if Tesla could continue adding just 2k cars more each quarter, 2017 would be 28/30/32/34 or 124k cars, 2018 would be 36/38/40/42 total 156k cars !
Break even is the most sustainable economic model long term. Avoid borrowing if at all possible.