What if you are not driving the car and neither renewed your licence plate and what if after couple of months of keeping the car unused you want to renew the plate again and restart the car?

The car should not be a problem... maybe the battery may be discharged but with an initially good battery, it may start without problems. If it doesn't, you should be able to either jump it off from another vehicle, or connect the battery to a battery charger to recharge it.

And as far as the plates/registration, unless you have outstanding fines or judgements, you won't have a problem renewing your paperwork at the DMV. Don't forget to check if your insurance is still current. You may also have to provide proof of insurance before renewing the plates.