פירוש על גיטין 7:1

The husband must be of sound mind when he orders [the writ of divorce] to be written. Therefore, if he was seized by melancholy when he gave the order we do not write it, even after he is well. Similarly, a drunk person, if he reached the level of Lot's intoxication, and he said, "write it!" we do not write it. If he did not reach [that level of intoxication], this is a case of doubt.

If he makes a condition on her "that you do this thing," it is to be assumed that he meant that she "do it some day." After all, he did not specify when she should do it, or for how long. How so? He says to her, "This is your Get , if you do work with me." "On the condition that you serve my father." "On the condition that you nurse my children" - if she does work with him, or serves his father, or nurses his children for one day, within the span of time that children nurse, which is 24 months, then it is a Get and she is divorced. Rem"a: And there are those who say that she needs to serve his father all the days of his life, nurse the baby until the end of the 24 months (Tur in the name of the Rosh). And if he dies even one day after she has begun to fulfill the condition, it is a Get (Tur). If the son or the father die before she nurses or serves them [respectively], it is not a Get . If he says, "...on condition that you nurse my son or serve my father for two years" she must complete the time that he specified. If the son or the father die in the time that he specified or the father says, "I do not want he to serve me" it is not a Get because she has not fulfilled the condition, and so too [any case] like this. And there are those who say that any [case] where the prevention [of fulfilling the condition] is not from her, it is a Get and it seems to me that in all these [cases], we rule stringently.

"Behold this is your bill of divorce if I don't come [back] from this point [mi'kan] for 12 months," and he didn't say "from now" [me'achshav] and [he didn't say] "on condition" [al menat], and he dies within 12 months, this is a doubt, and she must do chalitza and not yibbum.