There is no one right answer that fits everyone, but following are some of my own opinions on general situations that ought to at least bring up the thought, "Should I still try to save my marriage?"

Sexual abuse. This comes as close to an ironclad dealbreaker as anything I can think of. Still, as long as children aren't at risk it's a choice for the BS to make on their own.
Physical abuse. Another really, really bad sign. Having not experienced it myself, I don't feel qualified to comment much, except to say that significant counselling and very high boundaries in place would be a bare minimum to consider trying to salvage a M of this sort.
Repeated affairs. This is pretty bad, too, and certainly cause for grave concern. Very few success stories follow multiple adulteries, but there are a few so I can't be too dogmatic. How very hard it is to recover should certainly be considered.
Long-term affair. It is possible to recover, even from affairs spanning a decade or more, but just as with serial adultery it's very diffiult to recover successfully and should not be undertaken lightly, if at all.
Affair lasting longer than 2 years in Plan B. Since nearly all A's are ended by the 2-year mark, this is an excellent recommendation for when to move on. Some may wait more, and some may wait less, and that's fine. It's just that even normal relationships often hit a major change then, and the foundation laid up to that point plays a key role in what happens next. Solid relationships shift and change and adjust, while selfish, dishonest relationships almost always collapse.
Poor spouse material. If an A is a first, but an honest evaluation shows that the WS was never a good, loving spouse, chances are next to nil that they will change into wonderful people when the A is over. Run, don't walk, but that's just my opinion.
Short marriage. If you've only been married a year or two before an A starts, and especially if you don't have kids yet, getting out is usually your best option.

I'm sure others can think of many more. This is just a start.

Disclaimer: The opinions contained herein are solely my own, and should not be needlepointed anywhere.

Within an A recovery, it's not nearly so cut-and-dried.

About my only blanket recommendation would be that, if both spouses are on board and trying, to please give it at least two years. By that time, the light at the end of the tunnel should be within reach, if it's going to be.

If only one spouse is on board, especially if the off-board spouse is the wayward, it's a crap shoot: no timeline - it's solely at the discretion of the BS.

Ditto in the case of any false R.

That's so cool! I can crochet, but the word "needlepoint" has so much more oomph to it. I remember back when I could see little stuff, too.

(And thank you.)

I used to manage a number of large craft stores in the mid-west and was around needlework stuff all the time. (= alcoholic tending bar.) So you can imagine my collection of all the cross-stitch threads, all the needlepoint canvases, quilt kits and other such womanly arts that I collected up with my employee discount, meaning to do when I had time. Then I had laser eye surgery and couldn't do fine work anymore...sigh...

And sorry - no t/j intended. Continue with the list topic, please.

T/J's aren't permitted, because they aren't possible with me. My whole life is one big T/J, and I wouldn't know what to do if I wasn't hopping from one subject to the next to the next.

So I thought of one more, in honor of one of our esteemed MB'ers.

Your spouse tries to have you killed. I think for most of us this would be a dealbreaker right up there with sexual abuse, but hey, if you want to sleep with your eyes open every night for the rest of your life, I guess that's your choice.

Now, where were we with the needlepoint?

It is SUCH a good thing neither Neaksis nor I ever owned a craft store.

Addiction. If your spouse is an alcoholic, drug addict, or sex addict who is unwilling to address the issue, that is a deal breaker, IMO

Turns from human companionship to swine??

Well, that would be all of them, wouldn't it?