Snagged it from the Heroes of the Storm slider on Blizzard's new online press center, which seems to have gone back offline for the time being.
Sylvanas Windrunner, Chen Stormstout, Illidan Stormrage, Anub'arak, Nova Terra, Diablo, and a Witchdoctor are all clearly visible.
Edit: They released the full artwork over Twitter.
https://bnetcmsus-a.akamaihd.net/cms...3791597220.jpg