While I am a big fan of therapy, I do not think this situation as you’ve describe it is on track. He cannot move back in first just because he feels bad and wants to change. This doesn’t honor your daughter’s needs. This also isn’t a time for some collective therapy with you, your daughter, and your husband. He has significant therapeutic issues in front of him that are not a quick fix.
Endangering the welfare of your daughter is not a normal reaction to grief over his father’s death. He needs to stay out of the house, away from your daughter, and in therapy with an expert. Just like you said, you never imagined that he could do this — so you cannot make the assumption that he is okay enough to bring back into your home. If you are going to make an error, make it on the side of your daughter’s safety.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral