Are they keeping the payments current?
The loan will be considered in defualt if they file. It will report to your CRs as a major derog!
I would see if the lender is willing to release them from financial responsibility and see if you can become the sole account holder. YMMV here. May lenders are reluctant to do this but you can make a case especially considering you have kept payments.
If all else fails, refi the loan and remove them. If you cant refi, I would find a way to buy out the loan either via cash or credit. Either way, be proactive about this and spare yourself the agony of having a BKd account report.