How about this cast:
Emiya Shirou: Tohsaka Rin Caster
Toshaka Rin :Emiya Shirou Archer
Matou Sakura: Medusa Rider
Illyasviel von Einzbern: Shirouko Saber
Bazette: C? Chulainn Lancer
Random Magus: Medea Berserker
Medea: Archerko Assassin
Shirouko: Shirou with Illya's body. Avalon made it through the transfer. Convenienttly enough, it turns out Illya's body is actually rather superhuman after a growth spurt and some rough training. Adds a stat boost because of a contract with the World, and you have a Saber. Maybe. :sweat:
Berserker: Again, the unknown Magus dies very quickly , simply because he doesn't have the mana to manage a Berserker. When the contract is broken, Medea is freed from the Mad enhancement. She places safeguard around to make sure she won't fall to them again, and then crawl around until she find a Master. Maybe Kuzuki, Maybe someone else.
Assassin:Okay, I got nothing.:huh.: Medea botched her summoning, but in a different way? This is pretty much a rip off from the sword dancer doujinshi.
And as the mysterious eighth Servant, last remnant of the 4th Grail war: Black Saber