> by default the union contract goes with the sale. This means that by default MRL keeps their own seniority and work rules, but the unions will likely try to get them to match pay and benefits without the new draconian train crew attendance policy.

What I learned when still working and being an BLE minor official, when there is a merger, the resulting combined railroad must retain the union agreements of both RRs. However, if one RR purchases another (like the UP purchasing the SP in 1996), the purchasing RR is not obligated to do this and can implement its agreements on the purchased RR's employees (the UP didn't do this on the former SP). My suspicions are that the BNSF will maintain the MRL agreements on the former MLR employees because they are more "BNSF-friendly" than the BNSF's own NCC-based agreements.