Who knows if they'll continue to offer lifetime subscriptions going forward, but not honoring lifetime subscriptions purchased pre-merger would most definitely lead to lawsuits and/or disputes being filed with credit card companies.
SiriusXM got sued a couple years ago when they tried to say that the lifetime subscriptions sold by Sirius (prior to merging with XM) only meant for the lifetime of the device the subscriber was using at the time of purchase versus the lifetime of the subscriber. They (SiriusXM) lost.