The medication will delay his death not cure him. The medication will prolong his life not cure him.
Both versions work. I would choose the first. ("Prolonging life" seems macabre to me -- unnatural -- although I recently had my own prolonged.) Perhaps this is because the expression "prolongi
As far as grammar is concerned both sentences are correct.
But if you are asking from the positive/negative perspective; I would suggest that, The medication will delay ........is negative sentence And The medication will prolong..... is positive sentence. But your positive sentence does not look good to hear. We don't use that kind of language though it is grammatically correct.