Update 2/22: Reported by CinemaBlend, Marvel Cinematic Universe head Kevin Feige confirmed that James Gunn’s Guardians of the Galaxy Vol. 3 draft will be used for the film, despite Gunn being removed as director.
Feige said to CinemaBlend, “
influence was Guardians. It was Guardians. It was his input on Guardians and the Avengers films, as you’ve seen in Infinity War, and on the Guardians 3 script, which we’re still using. So you’ll see that influence.”
It remains to be seen how much of his original script will stay intact once a new director comes on board, but it appears Gunn’s influence will remain with the film regardless.
Source: IGN.com James Gunn's Guardians of the Galaxy Vol. 3 Script Will Be Used