Finally picked up the truck from the dealership after the head gasket repair. Final damage: $490 parts and $3,550 labor. Fidelity handled warranty coverage, so out of pocket of $300. The warranty definitely paid for itself on this one. I spoke with a service manager about the failure. He said it could just be a random failure, or that perhaps the coolant ran low and created an air pocket. I missed the coolant service at 100K, but I never observed any signs of overheating, even while towing.
I never did get into the Mach-E loaner. Turned out the dealership sold it several days before I picked up my truck. Supposedly they're in very high demand. I kinda have my eye on the Kia EV6 anyway. It's 800V pack adds 200 miles in under 20 minutes.