Just the insurance angle. The 26 year old airframe would be worth in the region of $10 to $15 million max. but would have very little chance of resale so possibly even less than $10 Million. Because of the low value Delta may only insure liabilities, (pax and third party plus War) and self insure the hull, another possibility is that, given the age of the airframe, its book value has been written down to zero.
If the hull is insured with underwriters then the decision to repair or write-off rests with the insurers, in consultation with Delta, Delta's options are then likely to be: accept the pay-out, minus the deductible/excess, (and possibly buy the salvage), or cough up the amount of the deductible towards the cost of repair. An incident such as this won't effect Delta's premiums at next renewal, their overall fleet value is far too large and this is small beer.