We are already rolling for severe miscasts. Mathilde is described as being exhausted and even travelling through the ship is difficult when relying on her windsight. And that was before she was struggling with muscle ache and milky eyes caused by her minor miscasts.
The update explicitly calls out that going back will mean rolling even more dice than this time. Never mind that we also have to count on potentially up to 50 Dawi, who are alone, scared and possibly drowning to obey a voice they hear coming from nowhere telling them to turn off any light source they have. That sounds like another roll to have them not discount us as hallucinations.
Mathilde has to cast a massively boosted fiendishly complex illusion (so increased risk of major miscast), followed by another up to 50 uses of substance of shadow. Not to mention however many times she has to cast marsh lights to check if everyone is still alive. And ensure she can find enough aii pockets to keep herself alive.
This is incredibly risky.
