You're not even approaching what would be considered a scientific and somewhat useful study.
You can move away from a platform without a complete stop. I've seen people who used to post on Facebook on a daily basis claim to leave, and then they use the platform less and less until you rarely see them. What also matters is the nature of their posts. If people who used to put effort into thoughtful engaging posts start to post trivial and unengaging content, that has a similar effect to no longer using the platform.
If this happens in large numbers, it would of course impact your advertising revenue.
You can move away from a platform without a complete stop. I've seen people who used to post on Facebook on a daily basis claim to leave, and then they use the platform less and less until you rarely see them. What also matters is the nature of their posts. If people who used to put effort into thoughtful engaging posts start to post trivial and unengaging content, that has a similar effect to no longer using the platform.
If this happens in large numbers, it would of course impact your advertising revenue.