"The [M&G Polymers v. Tackett] majority's rulings that ordinary contract principles apply, that lower courts should not construe ambiguous writings to create lifetime promises, that contractual obligations generally cease upon termination of the bargaining agreement, and that courts should not infer that parties intended benefits to vest for life when the contract is silent regarding their duration, clearly tend to tip the scale in favor of finding no contractual vesting. However ... there is still an opportunity for courts to rule in favor of participants when the CBA is ambiguous by employing the use of extrinsic evidence as advocated by Justice Ginsburg in her concurrence."