I was in an accident in January where someone hit my car from behind. We both had Allstate. He was found to be at fault, and his insurance paid for the car seat replacement in full.
Check with the manufacturer of your car seat. For example, I went to Graco and Britax websites, and these companies each have a very different stance on this issue.
Copied from GRACO FAQ Section:
"I was recently in an accident. Do I have to replace my child's car seat? There doesn't appear to be any damage."
GRACO ANSWER:
"Yes. You must replace your child's car seat if it was involved in an accident, no matter what. Even if there appears to be no damage to the car seat on the surface, the impact and force of a collision can cause unseen structural damage to the interior of your car seat. Any such damage may prohibit your car seat from properly protecting your child in the event of a sudden stop or crash.
Some insurance carriers will reimburse you for the replacement of a new car seat if it was in a crash. Check with your insurance carrier for more details."
Copied from BRITAX FAQ section:
"Q. Can I continue to use my child seat after it has been involved in a crash?"
A. "BRITAX recommends that the use of a child seat be discontinued if it has been in a moderate to severe crash. We further advise of the National Highway Traffic Safety Administration (NHTSA) position that it is not necessary to replace a child seat after a minor crash.
A minor crash is one that meets ALL of following criteria:
The vehicle was able to be driven away from the crash site; AND
The vehicle door nearest the child restraint was undamaged; AND
There were no injuries to any of the vehicle occupants; AND
The air bags (if present) did not deploy; AND
There is no visible damage to the child seat."
Check with your manufacturer to see whether your seat needs to be replaced based on the specific details of your accident.