Complex sentence: The lawyers advised management to maintain passenger service on all lines so as to not violate the charter, and thus the Georgia was perhaps the last railroad to operate mixed trains in the "Lower 48," into the Amtrak era.
Split into simpler sentences: The lawyers advised management to maintain passenger service on all lines, so as to not violate the charter. The Georgia was perhaps the last railroad to operate both freight and passenger trains in the "Lower 48" states, into the Amtrak era.