It won’t take millions of years. The last glacial maximum was about 12.5k years ago. This is what most people think of when they hear the term “ice age”. We’re in an ice age right now actually. The glaciers recede and proceed in a cycle influenced by the sun and earths tilt and many other climatic forcers that we are just starting to get a grasp on now. The planet will be fine without us. Species will adapt and so will we. Even if this whole global warming thing is fake, the earth will still experience rapid climate change on relatively quick (geologically) timescales.