A striker such as Olly G who can play in goal when your keeper is blue-carded would be an asset.
Otherwise: Raya gets blue card. Outfield player subbed, Rambo comes on. 10 mins later Raya returns. Either he or Ramsdale then plays outfield or if any subs and windows left, one of them is subbed for an outfield player.
You're thinking about it too much, pj.
First of all given that blue cards are for cynical play or dissent the chances of a keeper getting one are pretty small. Other than taking a player down when he's through on goal, when was the last time a keeper got a yellow? They're pretty rare.
And I'm sure the rule would be nothing more than if the keeper gets a blue the team has to elect an outfield player to take the 10 min off.