Edited for qualification.
https://www.npr.org/sections/thetwo-way/2017/06/27/534524024...
Nothing is stopping them. But they wouldn't have the monopoly on ads to cover them if their results are of bad quality.
I'm not seeing how anything would change. Google search and whatever other google branches will continue working together so it'll essentially be the same thing but with a different legal structure to appease everyone.
I mostly avoid it, but that's because I mostly avoid any Google service. All of them are bundled and I don't want some AI misstep to lock me out of the few of their services I care about. At this point some forced unbundling would bring a huge trust benefit to Google.
But anyway, it is very clear that the bundling of Google's monopolies on ads and search are a huge barrier to innovation and competition on both of those.