Most people say just sit out, but I'm not certain if I agree. I mean, if it's me I would probably want to make the money if I had a chance, so I would sit out. I also don't think it's right to suck out on someone with an "i have to leave" all-in, and sometimes it might happen multiple times. Then again, looking at the cards that people call with, I have to ask myself if it is totally the guy leaving's fault.
I mean, sure, a guy is leaving and probably doesn't have great cards, you've got k/9 off suit, hey, it's a king, it's a middle kicker, or mid-pair top kicker, straight possibilities, whatever your justification is.... the bottom line is the stats on not really in your favor in the long run unless you've got a pocket pair against no overcards, etc.
They don't call it a coin flip for nothing. A/K vs. 6/7 is barely 60/40, even if you're suited!. Every two cards have EXACTLY the same odds
of pairing up preflop. Straights are straights, flushes are flushes. All of those odds are figured into the equation. And when you compare k/9 to 8/4 let's say, and we'll even assume that k/9 is suited, say spades, and the 8 is a spade and the four is not, EVEN THEN, the 8/4 has more than a 1/3 chance of winning. Is it worth risking all of your chips when you know that in the long run, you've got less than a 66% chance of winning?
So yeah, of course people get "sucked out on", and in some ways have a right to complain, but in my book if you make risky plays, take responsibility and don't then shift the anger over to the guy that was leaving. Because let's face it, everyone loves it when a guy is leaving and they get dealt good cards. You're just begging for him to go all-in. And when someone pushes all-in because they have to go and you have rags and someone else calls and wins, everyone wishes it could have been them that had the hand.
It all comes down to greed, and putting reward over risk. And too often I see people call on coin flips and then complain about the loss. Just say no, just don't call, it's not that hard. Just like the guy leaving has a "sit out" button, so does everyone else have a "fold" button. And my guess is if there is an "I'm leaving" all-in donkey on your table, if he's really got to go he'll just go after he pushes all-in a few times and everyone folds.
If someone calls, they are putting themselves at risks and in my opinion are in no place to complain. Would you push all-in if the guy just did it out of the blue and didn't say he was leaving? If not then don't do it when someone is leaving and pushes all-in with rags.
Now, for the person leaving, I think the better thing to do is raise it up some pre-flop, but not all-in. That's enough to push out the people with mediocre cards (sometimes) and the guys that stick around probably have strong cards. So then if you totally miss your flop you can feel better about pushes a bunch more chips out at them, and then go all-in after the turn when you've missed again.
Play it like you're bluffing pretty aggressively, and if you tell people you've got to go they'll probably appreciate that because it helps push the odds in the favor of those with better cards, instead of everyone just having to rely on beating you in a coin flip. I've flipped heads 37 times straight before (not doing tricks with the throw position, catch position, etc. but just flicking it up and letting it fall to the ground), and in a statistics class a long time ago we once recorded 19 straight 3's when rolling dice in an experiment. That's at 6 to 1 odds each roll. Go figure.
Then again, a lot of people use the all-in thing as a lie when they've got pretty decent or better cards. They'll try to get calls out of people so they can have coin flip odds of doubling up. They ruin the credibility for anyone who really does need to leave, and wants to get rid of a few chips, but wants to do it in the best way possible to avoid suck-out injuries, etc. With the above scenario of dumping chips as you go, if you tell me you've got to leave, I know if you raise a lot I should call, and if you check I should fold because it means you hit.
Alas, we do not live in a perfect world after all.