[quote=@Andronicus23]
Even if the Legion lost at Hoover Dam, its entirely possible they still survived as a faction. A strong enough leader (aka whoever takes them over) could step into Sallow's shoes, claim descent from Mars as the next Caesar, and reorganize the Legion. 
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[quote=@Jeddaven]
<Snipped quote by Andronicus23>

I have to disagree. it's repeatedly pointed out in New vegas that the Legion is likely bound to fail, and with Sallow bound to die eventually, I don't see it not imploding, whether violently due to his death or more slowly due to simply not being a very sustainable society
[/quote]

Keep in mind that a lot of the speculation about the Legion's dissolution said that the Legion wouldn't fall apart all at once, and that it'd likely take a few years - if not decades. That being said, it could be reasonable to assume that there could be a few spans of competent leaders who would fill the shoes while the Empire crumbles apart. 

Roleplaying a crumbling empire like a Post-Caesar Legion will also give [i]tons[/i] of opportunities for roleplaying hooks, given the sheer geographical distance of the Legion. 

That said, it would basically take a complete reorganization of the Legion to make it stand a test of time...which itself is enough of a roleplaying reason to be interested in it after the events of NV.