Does the spouse have to pay the mortgage?

My mother is getting a divorce, however, no separation agreement has been established and no mediation as of yet. My step-father has taken all of the joint money out of my mother’s and his joint savings account. This includes $6,000 of her own dollars. Her lawyer advised her not to leave the residence until there is a separation agreement. He seems to be using the joint monies to fix up the house. He plans on retiring next year, selling the home, and moving to another country. In the event that he leaves the country after the divorce proceedings, what guarantee would my mother have of him disbursing her her share of the joint assets? Also, he seems to be accumulating a lot of debt on his own cards. Will her share of their joint assets have to go to repaying his debts?
My advice to her was to start saving all her money in a separate checking account (not to be combined with pre-marital assets) and not to give him any money towards bills, mortgage, and the like.

What can someone do for themselves in this type of situation where it is obvious that one party is squandering money away before a separation agreement is made?

Equitable Distribution (dividing marital assets) should be addressed prior to filing for divorce. If a party files for divorce and there is no claim for equitable distribution pending, nor has it been settled via a separation agreement, the claim is lost. Your mother should not wait until after the divorce (and after your stepfather has left the country) to address how the marital assets are to be split. So long as there is an order or separation agreement in place, if he does not abide by the terms of the order or agreement, your mother can either file a motion for contempt or sue for breach of contract.

As far as the post date of separation credit card debt is concerned, spouses begin incurring separate debt after the date of separation, or when they begin living separate and apart. Debt acquired after the date of separation is separate debt.