This will amount to several thousand dollars and if you do not pay they will take you to court, get a judgment and at that point they can attach bank accounts, garnish wages (if your State allows it) and file liens on any other property you may own like cars, boats, land and homes.
All of this activity will show on your credit for the next 7-years.making it very hard to get any other types of loans without making huge down payments, paying massive fees and State maximum interest rates.
Score wise you can look for between a 100-150 point drop depending on what makes up your score now.
If this has not happened yet do whatever you have to do so it does not, sell the car and get a loan for the difference.A repossession without a bankruptcy is one of the worst things that can show on credit reports.It will be like rain and snow, it will fall.