Debt Dispute Impact

Dear Experts please advise:
I have an insurance dispute with a car rental company amount to $11,000. Now the case is at the collection agency and I am trying to resolve with them or, eventually go to court with the creditor.
My questions:
1. What will be the likely impact of such amount on my credit score, if I don't pay? My current FICO is around 760. How long will the credit damage last?
2. Will this type of things (debt dispute, default in payment, damaged credit or court appearance) affect my immigration? I am applying for Green Card through employer.
Thanks a lot!