It is not. It appears to be dependent on the landing surface for one thing.
If you accept the maximum is 10 days then that contradicts the 72 hours or half life of 6 hours and must leave many more alive after that 72 hours.
Not really. It depends how many there are at the start (and where they land).
No, it isn't. The life expectancy is the average; not a half-life.
No, but it is not to do with half-life but the maximum life.
Of course it would take longer if it were to do with half-life.
Let's take the fifty people and a half-life of 25; it can't be much higher with the maximum life possible (maybe a little over 100 for a very few).
If 25 die at 25; 13(can't have half a person) at 50; 7 at 75 and 5 at 100(supposed maximum) - then the average (LE) would be only 46.
If you start with 100 then there will be twice as many alive between 75 and 100 but the average will be the same 46.
Yes, but when LE is 80, only so many can die young with the maximum age being what it is.
Yes, that's all very well but, nobody likes a smartarse.