You should not think of "durative" and "punctual" verbs as grammatical categories. They are semantic categories. The verbs are grouped by meaning.
And with categories based on meaning, there can be grey areas, or words that don't neatly fit in to one category or another.
For example "cure": You could view this as a "punctual" event, or a "durative" process. Now the usual analysis is that to cure someone you need to do various things to them. It isn't (or at least it doesn't have to be) a magic touch that cures someone, and so this has an internal process and is durative.
Similarly consider "kill" and "die". Killing something has an internal process. Dying does not. And so "kill" is durative, but "die" is punctual. [And yet people do talk about the process of dying, so even this is not completely black-and-white]
So the "rule" is to consider the meaning of the word, does it describe an event that normally happens in the blink of an eye, or does it describe an event that has an internal temporal structure.
Reference: I'm lovin' it