okay, try to follow
I mean, given your spread, what must the count be for the shoe in its entirety to have a negative expectation.
Let us suppose you are playing a 6D shoe with one deck cut off. Let us say that you are one deck into this shoe and have a running count of zero. Yes, you have negative ev on the next hand out, of course, but the ev for the shoe is still the average expectation for a 5D shoe with 1 deck cut at this point. You can simulate and find what your average win per shoe would be given your spread in a 5 deck game with one cut. Suppose another deck goes by, now 4 are remaining, and the running count is zero. You now effectively have a 4D shoe with one cut, a damn good game. Don't make the mistake of thinking that this equates to a 6D shoe with 3 decks cut, simply because 3 decks are out of play. In a game with poor penetration you don't get to count the cards that are out of play behind the cut card. In this case you have seen two of the three decks that are out of play. When you get to the point that there are only 2 decks left, one in front of the cut card and one behind, with an RC of zero, you have exactly the same game as a freshly shuffled 2 deck game with 50% penetration. This is not a great game, but better than walking around doing nothing, and actually a more favorable game than a freshly shuffled 6D shoe that is about to start. It took lots of arguments and sims to prove this to Don a few years ago. If you have seen all the cards dealt from a given shoe and have a running count of zero, at any point in the shoe with N decks remaining and Y decks cut you have exactly the same game as a freshly shuffled shoe that has only N decks with Y cut in the first place.
When you walk away from a table you are not making anything until you find a new place to play. You should do this searching while you are at your current table. Depart either when you have a negative RC and see another table shuffled and ready to go, or when the RC has gotten very negative.
If you are a flat bet Wonger then you will have negative ev for the remainder of the shoe at any point that you don't have the edge, since the expected true count after N rounds is always the same as it is on the current round. This is one reason that it may be good to have some spread, even a small one, for Wonging. Even a 1-4 spread generally has positive ev if a -1 TC departure is incorporated. He needn't immediately Wong out of a positive running count that has mild negative ev.