The 2020 rotation and the arrival of the new Standard Year will, as always, be decisive in Hearthstone.
Three expansions will rotate out of Standard mode (Witchwood, Boomsday Project and Rastakhan's Rumble) and this should create a real revolution.
While they'll still be able for playing in Wild mode, a lot of Druid cards from the previous expansions are going to leave the Standard mode, meaning that several different archetypes that are currently shaping the meta will be affected — or will even disappear.
Some of these cards weren't really used, but the disappearance from some others will definitely be noticed...
Witchwood
The Boomsday Project
Rastakhan's Rumble
The Quest Druid should continue to exist even without Loti and the Ferocious Howl, and might even get some new very good Choose One. The Druid Mec'thun and the Big Druid will mechanically come out of the format, while the Token/Treant Druid should take one hell of a kick in the wing. It remains to be seen whether Blizzard will continue to support the archetype in the upcoming expansion...
The Malygos Druid will have to renew himself completely after losing Flobbidinous Floop and Dreampetal Florist, and maybe even Malygos in the Hall of Fame. The current Embiggen Druid should not undergo any profound changes and will remain a fairly safe value.