The LBS will know when the time has come because of two major changes.
First, the WAS will have dropped most of the trappings of depression which made him an alien. Rather than feeling completely alone when with him, the LBS will feel that he "sees" and "hears" her. He will feel more comfortable in his own skin, able to relax and appreciate things external to his own concerns. He will also be comfortable and behave in a mature manner with the people he shunned while in selfish mode (including the LBS's family, usually). He will often be full of memories of what the relationship was like before he became depressed. It will feel as though the "old" H came back, shedding the angry, self-obsessed, restless, pleasure-seeking, self-pitying, blaming creature that inhabited him.
The other necessary change is in the WAS, who must have reached such a level of detachment from the marriage that she now feels confident that she can have a wonderful life even if the WAS never comes back. She will have "got a life" which inludes all the self-care, friends, activities, sports, hobbies and challenges she requires for a full life (balanced, if appropriate, with children and work)--she will have become the kind of person she admires the most. She will also have worked on all those issues that lead to conflict in the previous relationship--whatever fears or insecurities or anger triggers or things that couldn't be discussed she carried because of family of origin or earlier experiences--learning to recognize and take responsibility for them rather than allow them to be displaced onto other relationships.
What I'm saying is, you don't want the WAS to come home until both of you have had enough time to grow up fully. If he comes home sooner, the relationship will only fail. The time it takes is far less important than the outcome. Focus on finding happiness within yourself. You'll never regret that, whatever happens with your spouse.
