I made a post about this quite a while ago now. I proposed the idea that they might know each other. They both practise Dark Magic, they’ve both been in possession of the Darkhold and they’re both extremely long lived. iirc Morgan is older than Agatha, which would be a great connection between them if one was the teacher and one the student. Agatha did have her own coven, but after she’d killed them she could’ve run into Morgan and Morgan could’ve taught her Dark Magic proficiently. The Darkhold could’ve also been passed from Morgan to Agatha.
But to answer your original question, a meeting between those two could look like anything. They might not like each other, they might want to use each other, like I said they might be fond of each other and happy to be reunited. They’re both very powerful witches, so I could see a team up.
