A definite 'no' from me, at least for the vassalage case. Fighting in your liege's wars is part of the feudal contract. For the case of an independent ruler, I don't have anything against such a button, but don't really see a need for it either.
I think mortality in battles is pretty OK, too low if anything. On average, before taking traits into account, there's less than one in two hundred chance per combat pulse (ten days of combat). I.e. a ruler can lead troops for over five years of constant battle before on average dying (or becoming incapable). Definitely a risk worth taking for the piety and prestige, in many situations.
I think mortality in battles is pretty OK, too low if anything. On average, before taking traits into account, there's less than one in two hundred chance per combat pulse (ten days of combat). I.e. a ruler can lead troops for over five years of constant battle before on average dying (or becoming incapable). Definitely a risk worth taking for the piety and prestige, in many situations.