Since the end of the G4 of MLP is maybe for 2020 , does the artists who makes MLP content will stay on G4 or will draw G5 ?

I don't know, what ever they feel like. Probably depends on what the new ones look like.

Given that the fanbase has lasted as long as a decade, it's creative members aren't likely to instantly move on; even if there is new source material to work with. No doubt the most prolific artists will probably draw both, although there might be a noticeable decrease in both abundance and quality of G4 art, in relation to G5 art. However, this is largely dependant on whether the current fanbase takes to the re-branded version of MLP, as well as how many new members find themselves involved in a potential new community.

The question of art creation makes me wonder about the communities actions as a whole as well. I assume websites like Equestria Daily will continue to report on new generation content, both official stuff and fan generated, which might create issues with those who don't find themselves enjoying the rebooted version. Either way, it will be interesting to see the reaction, given the rich history of the brony community. This effect will likely be illustrated through the creation and viewership of any art that's made available to us all.

Also, you should probably rename this thread topic to something more appropriate. Just calling it MLP isn't clear about what you want to discuss.

I haven't seen any official news about the ending of g4 of MLP... or even anythign more substantial than rumors, honestly. there were the leaks, but those were ages ago. Certainly nothing like "2020 is the end"

Anyway.

Your question is treating artists as if they're a single hiveminded entity. They're not. every person is an individual with their own opinions.

Some people will take the ending of the show as an opportunity to bow out.
Some will fade away.
Others will keep on drawing new g4 art because they love g4 and the show airing or not airing has nothing to do with that love.
Some will stop in the few months after that.
Some will still be drawing g4 art in a decade.
Some will move on to g5.
Others won't.
Some will draw both.
Maybe g5 will be great and attract new fans, old fans, young and old.
Maybe g5 won't have the same spark and there won't be very many new fans.
Maybe g5 will suck and people will abstain from it.
Maybe it'll be different things to different people.
Maybe it'll need a season to get warmed up.
Maybe the first season will be the best.

There are so many maybes and variables here, that we just... don't know.