First things first, I've edited out one of the images as it contained content grounds for punishment, which I will deal with appropriately
Thing is, with this whole situation- the whole "GG" "rekt" fad is all over the place. This isn't something that originated on MCSG, or even in minecraft, to my knowledge. Many other communities within minecraft, and other platforms use the same terms. Plenty of YouTubers use these terms in gameplay videos, in chats, in tweets, and in things like "fake" montages. A lot of people see those terms used in a funny way, such as how some people often say things like "{occurrence} GG" or in previously mentioned montages meant to be funny, where "GG" and "rekt" are basically the only words you'll hear and see throughout the video.
This said, unfortunately, most people have caught onto the sour context of the word, and have used it in that manner. Most people use it with the complete intention to annoy, and upset people, which is often the exact reaction they get.
While I personally don't find it bothersome, I know the effect it has on others. Though I think of it as just a word, I know, and understand why it frustrates people. Dying in-game often lights a fuse, and a follow-up of "rekt" can really burn through that fuse.
Whether it should be bannable or not, I'm really not sure. From my personal standpoint, I don't see it as a big deal, but I know many other people do, and that's not something I discredit. Typically, the same people to use those terms would also go further, and end up being banned for doing something further.
In the end, I'm really not sure. Either way, I think it won't have a massive impact on the state of MCSG.
To answer your second question, I honestly think time will tell the tale of MCSG. People come and go every day, but with that said, I don't for see an ending anytime soon. MCSG will always have a redeeming value, and I think with new people joining every day MCSG has a long while to go