It is possible to renew your car insurance after expiry.
After your car insurance has expired you can still renew it and get your car insurance coverage back.
However there may be a lapse in the car insurance coverage and possible penalties such as fees.
Many insurance companies offer a grace period for the auto insurance and other insurance policies which is a short time period after the insurance policy has expired where you can reinstate the insurance policy without a new purchase.
Although if the insurance policy grace period passes you will then need to purchase a new car insurance policy which can result in you paying a higher premium or even result in a temporary lapse in the auto insurance coverage.
Once your auto insurance expires you're no longer covered and can no longer drive your vehicle on the public roads until you get the auto insurance reinstated.
You can get the auto insurance renewed after expiration by visiting the auto insurance office or calling their number and paying the fees and reinstating the coverage.
If you happen to be unable to renew your auto insurance after a lapse in coverage you may need to purchase a new policy or could change insurance companies.
I've had my insurance expire and was able to renew it again without any issues but the sooner you get it renewed the better.