How will IDFA deprecation impact Mobile Attribution companies?

Just to get on the same page with vocab, the "probabilistic" you are referring to is basically fingerprinting. IMO all of those types of technologies cannot continue to exist without user permission on iOS devices.

WRT how attribution companies play a role in this, they will start to build technologies on the aggregate data from SKAdNetwork (and other places) as signals to inform measurement and optimization. I believe this is where most of the technology will need to be focused on for iOS in the future. Developers still need to understand where to best spend their budgets.