The 'Safe Zone'
When the line of communication is consistent, say for a calendar year. That gives you a distinct and remarkable timeline. Holidays kills games. Disaster kills games. Quickies move on when the high goes away, which is valid if that's their motivation for gaming. Melodramatics lose interest when the plot has to become slow and sin;t skipping to the chase. I could go on. The point is ask questions. When people don't answer direct questions and beat around the bush, you're losing contact.
Game safety is (at least like) trust. You never know if you have it, you know when it's gone though, broken and dead. I feel safe in games where the players/GM are direct and address their problems and mine. When I say "Hey am I going to fast?" and others say something like "Yes, I'm hardly able to keep up!" or "Nah, I've been rearing to go." or "Holidays are coming up, we'll probably want to pick up the pace after that, but for now you're fine." or some variation of RL becoming more or less demanding.
Communication solves more than half of the problems in any forum. I had a person tell me they were a professional problem solver, but in fact she caused a dozen problems just by fixing something nobody wanted her to. "We need drama!" No, we don't. This isn't a soap opera. We just finished a major arch. We're allowing people to have downtime and plan on an independent level, to have low-key conversations and show the world has come to a calm. "We need fast posts people! How can we get people motivated?" Honey, people are active in PMs, see post #342 of this thread this is interpersonal time. And so on. Basically she left because the game was "dead" but it thrived after she was out of the picture and wasn't asking loading questions. Nice gal, just very misguided.
Keep the line of communication open. Ask a direct question, then post something, anything (not superfluous) if the cast sees both posts and isn't saying "hey. sorry. busy" or "I'm on my phone" or "PC broken" they are avoiding posting.
I have been without a keyboard and could use my mouse. My PC has been trashed and I went to the library. If they're logging in, they can type three words.
Once communication is broken, the rest is just dominos to the trend. Silence can be repaired and prevented, but communication is a great tool, like the wheel, to get things moving. Everything else is throwing rocks to get it to budge.
My safe zone is that period of time just after RL has been a ragged storm in troubled waters and the sky becomes clear. When I come back from long silence of not logigng in. Then I know hell or high-water the game will go on, by who remained on board. It's like a ship, keep posting, keep writing, even if you have thirty player cast, if even one is posting keep posting. If that player or GM is trying, you can double the effort just by being active. If they want another player, they can say "Hey, can we add/remove someone" if they're the only one posting then do it. Give some time for a refutation and then just keep going. Number 1 rule (for games) is have fun. Along that rule, in the fine print, is that the game must go on.
That's my opinion on the matter. Establish what people want, if they can't give that, that's on them. But if you don't want to GM tell people that, unless game is somehow consigned to some contract, it should be fun. It's not a job, and that bears repeating, it's not a job (to many at least). Just be honest, and clean up after yourself when you're done. People will move on. History dictates that truth.
Once you know this much, it doesn't need to be "safe" it's exciting and fun. A story can just end in mid sentence and leave you wanting more but be glad for the journey this far. Most good stories, I've heard/read, just end, your jaw drops and you look around...but that's it many games I've run successfully are on the ashes of dead games, mine, my friends' and even people I disliked but enjoyed their stories and carried the torch.
*shrug* Those are my rules I live by. I don't begrudge others for disagreeing, it's subjective, and that's natural. I just avoid them because they aren't compatible with me, and negatively impact my fun. I choose to think I would reciprocate the mood if I gamed with them. Know what you want, ask what others want. Discuss disputes. Invent solutions. Repeat every so often. >50% success right there.
Now, does that help? Even if only some parts contributed. Even if just by you thinking, hey I disagree, but that does beg the question...
If ask enough questions, and give enough input, million-to-one chances of a match are negligible...they happen every month. You don't need to have a formula at that point.