How would sanya react to meeting a greater daemon that isn’t one of the fuzzes? And how would said daemon or daemons react to meeting him?
Sanya after < month of adventuring with Fuzzes: still somewhat scared of anything Warp-related, suffers from an identity crisis of being a good imperial lad and traveling around with daemons and Xenos, unknown to the world at large.
Sanya after a few years of adventuring with Fuzzes: through osmosis learned enough to probably be able to proofread neophytes cultists' essays on Chaos, accepted his weird position in the world, figured that it all just means he can make friends on both sides, he and his merry "technically-a-warband" are known in some circles, got his first wanted poster published.
Sanya after a decade of adventuring with Fuzzes: tries to rehabilitate Skarbrand to society as a casual side project. Yes, it involves cooking and An'Hangra helping around. Made so many friends around the Galaxy. Thriving. Some sort of an urban legend, that in the retelling is both more and less unbelievable compared to an actual thing. Might be considered either a Living Saint OR Chaos Chosen by especially radical fans.
Essentially he is still just a very kind guardsman.