Google is your friend.
From BMW:
Paintwork Warranty
The paintwork warranty covers your vehicle against defects such as blistering, discolouration or staining of the visible surface of all painted body panels occurring as a result of faulty manufacture or workmanship
for a period of 36 months from the date of first registration without any mileage limitation.
All paintwork repaired under warranty must be carried out by a BMW Approved Bodyshop.
Although modern paints are durable and resistant to many external hazards, they cannot reasonably be expected to be totally resistant to all. You should therefore take particular care with your paintwork if you live in or near an area where industrial fallout is prevalent. Please read the relevant section in your handbook on paintwork for more details.
Bird lime can have an extremely corrosive effect on your paintwork and should be removed as quickly as possible.
Since damage caused by industrial fallout or bird lime is not a fault of manufacture, this cannot be claimed under warranty.
Anti-Corrosion Warranty
All new BMW cars registered from 1st January 2004 are covered by a 12-year anti-corrosion warranty against perforation by rust.
All repair work carried out under the anti-corrosion warranty must be carried out by an Authorised BMW Dealer or Authorised Repairer. The warranty covers corrosion which occurs from inside the metal panels or box sections of the car.
The warranty does not cover corrosion caused by neglect, accident damage, stone chips or other external influences.
Maintaining Your Anti-Corrosion Warranty
To ensure that any warranty claims are processed quickly and efficiently, please observe the following guidelines.
Your vehicle should be inspected at normal service intervals as recommended by your BMW service book.
Paint or body damage identified by the dealer during these inspections, including any to the underside or under body protection of the vehicle, must be properly repaired to BMW standards.
Claims cannot be accepted for perforation that occurs as a result of unrepaired or improperly repaired paint or body damage.
Vehicles which undergo major accident repair work during their anti corrosion warranty period are still covered by the warranty provided:
a. The correct BMW corrosion prevention methods are used.
b. The repair work is carried out by a competent repairer to BMW repair standards.
The warranty does not apply to parts, panels or materials that have not been approved by BMW and the BMW Dealer or Authorised Repairer reserves the right to refuse claims where defects have occurred as a result of using them.
Where your vehicle has been involved in an accident and requires bodywork repair this should ideally be carried out by a BMW Approved Bodyshop. In this way you can be certain that your vehicle will be rebuilt to original standards of safety and quality. You can then feel confident that the integrity of your anti-corrosion warranty will remain intact.
So, this confirms that your car won't be covered given the damage you've described.
HTH.