You will have to pay for any repairs to your lease vehicle if it's involved in an accident and any work carried out must be done at a garage which is approved by the leasing provider. Leaving any damage until the day when the vehicle is due to be collected will result in an expensive charge in order to get it fixed.
A maintenance package will only cover routine servicing and wear and tear issues, so won't protect you for damage caused as a result of an accident or driver error. In the event of your lease car being written off or declared a 'total loss' by your insurance company, you'll need to contact the leasing company or provider immediately.
Afterwards, the funder will require written confirmation from the insurer, and a 'settlement figure' for any outstanding finance on the car will be worked out.