My firends husband died recently and she has found out that he owes over $600,000 to various companies. For example, he had brorowed $ 10,000 from

She should probably hire an attorney to help her because there may be liens or other encumbrances on property that were done without her knowledge.  for the most part, she might be able to avoid paying the charges, and have her husband's estate declared to be "insolvent" and discharge the debt of the estate in a manner similar to a bankruptcy discharge.  The ability to do that is going to depend on what assets are in the estate, what things, if any she owned jointly, and the nature of the debt. 

She should hire a NJ estate lawyer. No, she should not be liable unless she co-signed. An estate may need to be opened. If there are insufficient assets of the husband to pay the debts, the court will discharge the claims.