In mergers/acquisitions like this, what used to happen is that the FTC/etc would require that they continue to sell or support all comers for some period of time.

For example, when Google bought ITA, ITA was required to continue licensing the software on "commercially reasonable terms" to other people.

See https://www.wired.com/2011/04/google-ita/ for an example.

Now, whether this will happen in today's FTC/DOJ, no idea.

But that is one traditional path here.