Here's the problem with that reasoning. A household of one does not cost half of the amount that a two person household does, it costs more. In fact, when the census normalizes income for household size, it uses the square root of the number of people in the household. Thus, a one person household is 1^-2 or 1.0, a two person household is 2^-2 or 1.414, a three person household is 3^-2 or 1.732, and a four person household is 4^-2 or 2.0. If we take the reciprocal of these, that means the expenses of a one person household are about 71% of the expenses for a two person household. (1.0/1.414 = 0.707). So, if your friends have equal pensions without survivorship rights, then when one dies the income goes down to 50% of prior, but the expenses are still about 71% of prior.