The release of Guardians of the Galaxy Vol. 2 on Netflix is part of the on-going deal with Disney that has seen previous Marvel movies, as well as animated features, released on the service.
Disney isn’t looking to start its service until sometime in 2019, so we could have some time, but whenever the current deal expires, Guardians Vol 2, and everything else will be gone.
Having said that, we know that since Disney is working on the company’s own streaming service, Marvel, and all other Disney films, will be leaving Netflix at some point in the future.
Movies like Captain America: Civil War and Zootopia are still available on Netflix, so there doesn’t appear to be a short window for their availability.