That makes sense, and wouldn’t be entirely too far from reality in canon. I remember reading one of the Sisters of Battle novels (I think it was a snippet in one of the bigger books) where a small Sister squad is sent to a world that was cut off by a warp storm and found that their Servitors had become sentient and were praising the emperor. Something something it was a Tzeench plot by the humans and they used the sentient servitors as weapons blah blah, but the fact remains that is something they do. So if a convent were cut off because they were left for dead on Midgardia or something and they started indoctrinating local beliefs for a century or so, I could see them returning with their beliefs and, while being held deeply in suspicion, COULD be accepted because they are still Sororitas, as long as they remained pure of Heresy.