The Ranger Unification Treaty specifies that the Desert Rangers would join the NCR as long as they protected the dam, New Vegas, and southern Nevada. Depending on how you interpret that, it could mean that in any ending where the NCR leaves that would constitute a breach of contract and cause the Desert Rangers to secede, probably taking a fair number of NCR rangers with them. Far reaching political ramifications there, especially if the rangers stand in opposition to whatever regime controls Vegas.