NP-can't find anything definitive but it seems claims would be contested by insurers (big surprise) even if BI insurance was in place by teams.
Whether MLB opens the 2020 season or not, they will likely be able to use changes in the tax law due to CARE Act to use NOLs to carryback 5-years and offset taxes in prior years.
As an aside, and with the proviso I'm not a tax guy or accountant, but its possible that a lot of '20 expenses may be non-cash (depreciation, amortization, write-downs) and a postive cash-flow could be generated in that $100 in NOLs could generate up to $35 in federal tax refunds. So its conceivable not playing baseball could be a net cash-flow positive event.