Ok then: if the 38yo husband took his increasingly unaffordable meds of choice and told you in a period of lucidity that he wants to die rather than suffer a lifetime of violent psychosis, drug-induced delirium and likely debt, or as you might call it "any quality of life is irredeemably lost", would you let him? Do you have another excuse for why he still cannot make that choice for himself, why he will never be able to make that choice for himself?

First you said they can't do it because they're mentally incapable of making the choice, now you're discussing whether a suicide is "clearly defensible". It doesn't matter if a suicide is "clearly defensible" or not. People don't have to defend their choices to you. That's the point of having the freedom to choose.