Sorry to discourage your dreams but the Ninth carried on according to links in the Internet before finally disappearing as most legions eventually did.
Chances are a lot of the rank and file of the Nona Hispana were Celtiberians and relatives of their foes in Britain. Match that with the almost neurotic discipline of the Legion and you have the kind of fighting force which can face odds of over 10 to 1 and win.
Fnatasy and fact get conflated in the production of a good novel, e.g. the Real King Arthur and the character in Le Morte D’Arthur.
I'm sure the movies will still be good fun, though.