RedBaron...I have three words for you: document, document, document.
If you're headed for a legal battle and/or mediation, you need documented proof that it isn't safe for your AW to be alone with her children. This isn't about "winning", it's about what's best for the kids, i.e. a healthy and sane family life.
And you're right...as nice as it is to have your in-laws concerned and involved, this is your decision to make, especially because you have to consider the safety of your children. To poorly translate a Québécois expression, "they can wring their Kleenexes all they want", but in the end, none of you control your AW's actions, whether she chooses to drown in a bottle again or complete suicide.
If I were you, I'd consult a few other lawyers to get a good lay of the land, legally speaking, and clearly discuss what can be done to prevent your AW from coming home after treatment. Others on this board have dealt with similar issues so perhaps they can offer advice. Some have left with the children, and others have petitioned the courts for emergency use of the family home. Alternately, you could call the rehab she's in and ask them what kind of options they have post-treatment (perhaps a sober living facility)...
In the meantime...get thee to Al-Anon! It'll definitely help support you in this difficult period.
Keep posting!