First of all the easiest way to ski powder is to never think about slowing down even you need to slow down you do though line first and then smearing second which is exactly my train of thought for skiing groomers as well I never want to slow down but if I do i do it though line first and then though skidding or brushing second. BTW you can not smear in powder on skinny skis.
Honestly once I get going in powder snow I truly do it ski it pretty much the same way as a groomer. I even still balance mostly on the outside ski even though that get alittle less biased in powder.
Honestly the fact you asked what happens when we need to slow down mean you do not understand skiing. We never choose a line that makes us think about slowing down or at least hopefully we do not but the world is not perfect and some times you need to smear.
I ski very round line till its get tight then I throw them sideways or I just straighten them out and hope for the best with Jedi like reaction times and incredibly strong core and legs and I can almost always recover. It easy to ski powder on wide open steep face trying doing it low angle woods that are anything but flat terrain and with tons of trees to cross block out of the way.