Commentary for Kiddushin 119:9

Abaye says that in principle R. Yohanan would hold that if he says “From today and when I die” this would not be a valid get and she could have yibbum (because she would be a widow). But he does not allow her to undergo yibbum lest people think that the same would be true if he says, “From today if I die” which is definitely a valid get, since this is certainly a stipulation.