I was making some assumptions in my statement, they are somewhat logical.
The Emperor "should" know one of his Primarchs is coming to Terra. That should be enough to get his attention to inform the leader of the Custodes to have him, and probably the High Lords as well brought before him. From there I have no idea the outcome.
If by chance the Emperor doesn't summon him then I do think the High Lords will try to stop or hinder the Primarch as much as possible.