practically yes, in the epilogue it was just a flashback of when jooha was waking up from his coma w the fight from pilwon, the last panel is dooshik swearing that he would always keep jooha happy - its safe to say they drowned as there is no other answers at all.
did they both drown? why make him lose his memory if he's gonna get it back in the same chapter?? this ending is so silly lmaoo