There are a lot of factors that go into this. These issues range from medical costs to wage loss, etc. Experts may be needed from the medical condition to vocational experts. It's really not something that been commented on a message board. Policies can stack, there may be med pay available. I'd strongly encourage you to take advantage of a free consultation with a lawyer. At least do your homework and weigh your options accordingly.
I don't see why they wouldn't pay for your injuries if you were rear ended and you were not at fault. Have you been to the doctor? If not, then maybe that is what they mean. Usually you need to have some medical treatment in order to recover for your injuries. If no medical then the insurance carrier is not likely to pay you anything over a few hundred bucks as a nuisance settlement.
Generally have 1 year to file for a change of condition for the worse. This is a VERY fact specific issue with your case and really can't be answered on a message board. Call a lawyer ASAP to give all the details. Excuse typos- on my phone
First, I am sorry for your loss. Absolutely a horrible situation.
Second, you probably cannot "sue" the employer but you could still file a SC workers comp claim assuming that employer had 4 or more employees. Just because they did not have comp insurance does not mean they are not responsible. You can still file with the workers comp commission and proceed against the uninsured employer's fund. if successful then the uninsured employer's fund would pay the benefits and then assess those...