Although the term is usually associated with the teaching of grammar, a prescriptivist is one who believes that there are tenets, conventions, and essential features—in sum, prescriptions—that individuals engaged in some activity must adhere to for their works to be legitimate. In contrast, a descriptivist is one who takes the work of those who identify themselves as engaged in an activity as the primary data from which the current features of the activity are to be deduced. Therefore, a fanfiction prescriptivist for our purposes is someone who believes that there are certain essential features that a Daria fic must have or else it is illegitimate—i.e., not a Daria fic to begin with.
The issue is argued once every few years within Daria fandom, typically resulting in not outcome but the argument itself. Most Daria fans have wide tastes in the types of fanfic they will read. A post-canon story is as likely to please them as any other, so long as the story is well written and contains elements identifiably "Darian." The primary irritation on the part of the prescriptivists is that certain stories are not enough like the original series to merit being labeled as "real" Daria fanfiction. The primary irritation on the part of everyone else is that the prescriptivists assume the mantle of being the final authority of what is "real" Daria fanfiction and what isn't. Frankly, things would go a lot better if everyone read what they enjoyed and ignored what they did not. Prescriptivists tend to leave the fandom sooner than other fans do, a consequence about which few complain.