As a former property insurance broker whose clients had big claims ($100Mish) and worked around people who handled the real big claims ($1B+), I can't really tell you with any specificity of how this will play out. All I know is that it will be a huge mess, and the lawyers will argue in court for several years.

Ultimately, someone will have to pay to rebuild the bridge. In the event of really big claims, it almost always end up being whoever has the deepest pockets. The process of discovery will list out who all the owners are and how much their policies cover this claim (whether intentionally or not!).

As counterintuitive as this may sound, the insurance and reinsurance companies are actually pretty well equipped to handle this type of event. The underwriter(s) on the other side of policy will have to report the claim to their boss and the report will show they followed company guidelines. The boss can only shrug her shoulders and say "welp, can't be too mad because this is the business we are in." No one is particularly thrilled about paying the claim, but these situations are exactly why insurance was created. (For context, the "small" claims of $1M -> $10M hurt the most because they are the ones that throw off underwriter's models the most and cause the most unprofitability)