My colleague asked me to review your question.
The botXXXXX XXXXXne is that if your roommate files for Chapter 7, and the case is a "no asset" bankruptcy, which means that there is nothing that any creditor could collect, regardless of whether or not they are named as a creditor in the bankruptcy petition, then you would be on the hook for the entire lease, and your former roommate would have no further liability.
You would not be able to sue your former roommate under any circumstances. Only if the roommate has assets that could have been used to pay a portion of your claim would you be able to sue, after being omitted from the bankruptcy petition.
Based on your likely circumstances, I'm betting that this is a "no asset" case, which means that unless you, too, intend to file bankruptcy, that you will be stuck with the entire lease.
Hope this helps.
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