I know aspect can be categorized into perfective and imperfective, but I'm just curious whether the example "John hasn't gone to Paris" is still perfective or converted into imperfectve?
In English, there are only 2 aspects: continuous (I'm reading, I wasn't reading, I have been reading, the book is being read) and non-continuous a.k.a. simple (I read, I didn't read, I have read it, I haven't read it, the book wasn't read). Whatever you do, you will never convert an English verb into the perfective aspect or into the imperfective aspect, English simply has no such categories and has no means to express them.
The Slavic languages (Ukrainian, Russian, Polish, etc.) do have perfective and imperfective verbs, but note: verbs, not verb forms. Slavic verbs go in pairs, perfective and imperfective, this means for each action, for each state of being there are at least two different verbs. For example, “to sit” is not just one verb in Russian, it's two verbs: сидеть (sidét’) which is imperfective and посидеть (posidét’) which is perfective. This verb pair differs by the prefix, other pairs can have different suffixes, for example “to push” is imperf. толкать (tolkát’) and perf. толкнуть (tolknút’), other pairs can even have completely different roots, like “to take”: imperf. брать (brat’) an perf. взять (vz’at’). When you're not a native speaker and you're learning a Slavic language you'll have to learn at least 2 Slavic verbs for each English one.
• The meaning of the perfective aspect is that it shows the action as having either a beginning or an end, so the perfective verbs are to be used in sentences like “He went to the store (meaning he took money, a bag, and left the house)” or “In the evening he came back home (meaning he opened the door and entered his room)” – beginning of action in the first sentence, the end of action in the second one.
• The meaning of the imperfective aspect is that it shows the action as going on either at a particular moment or the action happens regularly, all the time, even forever, the main point is that there's no beginning, no end.
Imperfective verbs are to be used in sentences like “I love you (now and in general)” or “I am reading a book now”, or “I see him every day”, or “Yesterday at 9 am I was driving to the office”.
Your sentence “John hasn't gone to Paris” is in the English non-continuous/simple aspect, but it is neither imperfective nor perfective, it hasn't got even a tiniest hint at whether it implies the beginning/end or not. It can be translated into Russian in either aspect. If the situation of the sentence implies ‘ever’ then it'll be imperfective Джон не уезжал в Париж. If the situation implies ‘yet, so far’, or some obstacle appeared which prevents John from going to Paris, then it'll be perfective Джон не уехал в Париж.
Just as it is impossible to make the Russian word кот (kot) “cat” definite (‘the cat’) or indefinite (‘a cat’) since the Russian nouns have no such grammar category as definiteness and there are no articles in Russian, so it is impossible to put English verbs into the perfective and imperfective aspects. The English verbs do have the category of aspect, only the English aspects, continuous and simple, have nothing to do with perfective and imperfective.
Also, it's very important: the English perfect (have been, has done, have been waiting, has been built) also has nothing to do with perfective and imperfective. Negation doesn't turn perfective into imperfective, perfective and imperfective can both be negative and can both be positive. The Germanic languages including English have no perfective and imperfective aspects.