Raubahn's a GLA by training, he wouldn't know how to wield a gun (besides, Ul'dah doesn't even use firearms, that's a Limsan weapon). More likely it's just going to be like how Kreia fought in Knights of the Old Republic II after she lost her hand early on in the game - she just fought with her remaining hand one-handed style.

I guess it also means Raubahn would have to sacrifice Tizona for a much more lighter sword as those things he has are huge, cumbersome and unwieldy.