I believe it's unlikely that we'll know the manner in which these costs will ultimately be apportioned between NS and its insurers (and others), for the following reasons:
It is my belief the terms of NS insurance coverage are confidential, except to the extent NS and/or their insurance carriers would choose to waive confidentiality.
Prominent among these terms would be the NS "Self-Insured Retention" (deductable). A typical Class I railroad, when I was directly involved in review of insurance terms in the 1990s, would have a minimum SIR on the order of $25 Million. It's entirely possible this value has since changed, perhaps substantially.
In this case, there are significant questions of third-party liability which complicate any attempt to forecast apportioned total costs among the involved parties.
For these and other reasons related to duties of disclosure, it would appear likely that projected costs will continue to be the total costs of this casualty for the foreseeable future.