Been there, done that, twice :o:doh: It is better to work towards staying together, but she sounds like she has already made up her mind, so your friend has some rough times ahead. As others have said, stay calm, be reasonable and get a legal setlement.
On the % question, rough rule is 50% + 10% for each child, but that includes your super. As you can't cash in your super until your retire, the % can go negative :o on the liquid assets, at which point you can apeal for fairness. Lawyers will drain the accounts and can often cause you even more grief, but it is worth getting at least advice as the laws change and it is always better to be in an informed position.