You can use "a comic" (no s at the end) to refer to a comic book (look at the example in Loob's post 5 above) or a stand-up comedian (He has been a stand-up comic for years).
Not in this sentence. You need comic strip here.For example, in the sentence "A comic strip is a set of drawings telling a story..."
is it possible to replace comic strip with comics
In this sentence, it should be a comic strip."A comics is a set of drawings telling a story..."
or should it be comic then?