Thats why you have the team who tracks the capsule by plane, they jump out with a raft that can survive several days on rough waters. The capsule is pretty sturdy I assume to stay in for some time.
Scott Manley's latest video ( https://www.youtube.com/watch?v=R-HOQrinzlY ) says the capsule should be able to survive in the water for at least 24 hours at minimum, but probably longer.