How should I make use of this broken patio?

I recently had a stump removed for a tree that ruined the slate/cement patio in my backyard, and multiple pieces of the patio were removed. I’m trying to make the best use of this space without having to remove and replace the rest of the patio.

I’m currently contemplating adding a gravel extension to the patio to hide the broken parts and turn the old stump area into a fire pit. Does anyone have experience with a transition of materials like that? What gravel type would you recommend to minimize how ugly it is? Finally, does anyone have ideas for a “retaining wall” for the gravel as the grass/dirt currently slopes down around 4-5 inches from the patio?

Please pardon my not-to-scale illustration.