what can I do to avoid this situation
Your best bet would be to hire an attorney and file a declaratory action against your insurance company to ask the court to determine if there is coverage or not. My understanding of the law is that once you complete your task at work, and are returning home, you are not considered to be on the job. So if you had finished working for the day and were returing home, your insurance company may have improperly denied your claim. But the law on this issue is very fact specific, and must be looked at on a case-by-case basis. This is why it is important that you sit down with a lawyer familiar with insurance law, and discuss your particular case with him/her, so that they may properly advise you as to how you should proceed.
If you do have a judgment entered against you, and you dont pay it, a lien could be placed against you and a security suspension could be levied against your drivers license, meaning your license is suspended until the security lien is paid. Doesnt happen in every case, but there is the possibility, so it is at least worth you sitting down with an attorney and discussing your case.
Best of luck.