In marriage one spouse can keep the image of the good family in front of society, family and friends but that is not saving as there is nothing to be saved any longer, except reputation. Most answers above say it: "it takes two for tango" and I agree that no solo efforts can safe the union of two unless both are willing to fix it.
I think that one spouse can make a huge impact on a marriage by identifying problems and looking for solutions. Changing one partner's behaviour will alter the relationship. However, if things are really bad, I do not think that a marriage can be saved unless both people are prepared to work on it.
I highly doubt that. After all, it takes two to tango... You may try everything in the world to make your marriage work but you cannot do it all alone. Both parties need to make efforts at solving their issues. Making all the efforts is like fighting all alone - not worth it and def not recommended. But if your partner shows any signs of saving the marriage, then it would be wise to consider counseling. Professional marriage counseling can help big time.
It would be nice to think that anyone can save their own marriage just by wanting it badly enough, but it’s not a task that can be accomplished single-handedly. Marriages are, at their core, a partnership, and they require the efforts of both partners to succeed. When one of the married parties no longer wants the relationship to continue, any effort at salvaging it will be futile. Some spouses may try to convince the other to work on the relationship, but after a certain point, continuing to press for saving the relationship can be considered a violation of the other person’s boundaries.
I think some couples find themselves in these situations and don't even recognize it until it's too late. All of a sudden they look at the life that has been built and think "I'm alone in this." I think when things are bad, one person unwittingly takes on a much more active role in the relationship while the other person tunes out, but this almost never works. It may work for a while, maybe even years, but ultimately the person putting in the effort, doing all the "saving" will get exhausted and want a different solution.
Absolute cooperation between the two spouses is necessary. Even when the problem is supposedly the fault of one of the persons, it still is going to require the patience and understanding of the other. Whoever needs to make the behavioral changes is going to need support and maybe even direction.