In my opinion, there is a distinction that needs to be made in that a player that registers for a tournament and does not even login to the client to play at all is different from a player that logs into play a tournament, and has to sit out for some real reason, vs a player that logs into a client to play a tournament, and then decides to sit out for a length of time to gain an advantage.
In the second and third examples, the player is actually at the computer, and at some point in the tournament is active in the game, plays a hand, and then decides to auto fold. It could be that the phone rang and didn't want to lose their timebank. It could be that their kids were going to bed and they wanted to go do bedtime. It could be that the internet goes out. It could be that their laptop's motherboard fries mid-tournament. OR it could be that they know that there are short stacks and they don't want to be tempted to play a hand in order to ladder up.
In every one of those cases, you can't punish them. They logged into play, they played something, and then they sat out. Whether they sat back in is irrelevant in my opinion because they showed up and took their seat. Now in league, just like being in the money in a MTT, sitting out and laddering has an advantage. But...can you punish someone whose motherboard fries on them mid-tournament and take away their 4th place when they started sitting out with 9 left?? (May know someone this happened to....). I can't in good faith penalize them. Contrast that to someone who folds every hand on purpose - even AA. They aren't sitting out but are doing the same thing. Can you penalize them?
Now...where I have the issue is those that register for a tournament and fail to login at all. This person may have payed for their seat -
real money or play chips - and don't even play a hand at all to attempt to seek the same advantage. The difference is that there's no effort to play their hands to the best of their abilities - rather they are hoping that they can ladder up without bothering to play.
Again though, this is tricky because there are circumstances that someone could register, not show up and not play. Again, personal experience, but I registered for a league game on Thursday, and got home Friday night around 40 mins before game time. My internet was out. Totally, and not coming back. I couldn't play the home game on mobile, so I had to create a hot spot, connect the laptop to it to unregister from the game. Had I gotten home 10 mins before I may not have had enough time to get out of the game, and I would have gone the entire game without playing one hand. And I know others pre-register because they get home after late registration is over, but not so late that it makes no sense for them to play.
Again, how do you punish those that lose internet entirely, get caught at work late, stuck in traffic, or who are making an honest effort to play, but for some reason can't vs those looking to gain an advantage.
Some sites will boot you out of a tournament if so many levels pass and you haven't logged into the client but Stars isn't one of them. Policing this is impossible - we play in an online world, not in a brick and mortar casino (although this would be a riot doing this league live - you, me, Shel, Trish and Dave aren't that far apart, and Devon and Jeremi aren't too far) but you get the point.
My only recommendation would be that anyone caught doing it more than one get questioned to ensure the effort is legit, or suggest that they play a day that's more convenient for them. But ultimately, there are too many honest variables to punish those that decide that auto-folding AA is a +EV strategy.