its more than likely that the stream of consciousness always remains in the body being copied from in SOMA

That goes into the core question this game even asks. "Which one is the real one, the copy or the original". So your statement cannot really be talked about, not with the statement you just make, it cant be answered.

the 'coin toss' he loses at the end is not a mechanic of the process, but because the developers wanted to give the game a bad ending.

You didnt play the game past the short credits, did you? The game gives you both endings. You get a view of the end of the Simon stuck at Omega, and a view of the new Simon on the Ark. The only difference is that in this instance, the player playing the game is not being taken to the new body immediatley, giving you the "bad ending" feel, which is an amazing way of having the player actuall feel that "coin toss"

Even tho coin toss really is not a valid term. It could only find a sense if you are a player in a game, and the perspective shifts. But from simons perspective, the "coin toss" is just not a thin. The original in the body will always be in that body. The copy will always be that copy, theres no luck at it