I agree consult with a lawyer on this. The first consultation is usually free so write down all your questions before you call. You can also check with some colleges for speaker/events. Some colleges offer or have an attorney to come in one day a month or week to answer any legal the students may have.
You may also contact a free legal-aid office or you county bar association. Most cities, and counties have them. If your in the service or your spouse is contact the military law office and they should help you.
There are so many things to into consideration in order to answer this; i.e. how long have you've been married, employment for both, When was the 401k made/purchased, if children are involved. Bills owed and ongoing, circumstances of the abandonment was it just; went out for a pack of smokes or loaf of bread and didn't come back. Or were there things that lead up to the person leaving. Fighting, arguing, nagging consistently daily so much that it went on into the night. That they could not get proper rest for work.
So they had to leave, for the sake of their health and to get the rest they needed in order to perform their job duties. In that they could provide for their family. This has happened before, and the judge ruled in favor of the person that left. They had people come in that didn't even like the person that left to testify to all that. Everyone noticed a chance in the person, that they has not been to sleep. Persons boss wrote letter, stating how the persons perfect job performance went down very quickly. They had medical reports from doctors family and psychiatrist.
So call an attorney for this one. That is the best place to start.