No happy endings as we define them, not even bittersweetness. Markus has the happiest endings so far (Project Mayhem ending where you are the leader instead and get approved by him with the hope of him returning and his true special ending).
One for Randal that's kind of meh is where you side with Andrei, make a deal with Lazarus and let him kill Andrei afterwards choosing to look for Randal. You have to make your headcannon that MC will find him one day and maybe have a happily ever after.
Heath will always be tragic, either he disappears, cuts himself off from reality or well, becomes an angel.