it will grows back, I recently bought a sen, she is about 11", when I saw her in the lfs, she lost both of her Nostrils, I guess it was the tankmates, but I was interested in her so I bought her. Few days later in my tank, those Nostrils grew back, and now she is back in action, I mean she is fatter
yeah my largest sen had one completely missing when i got him and now it is halfway regrown after having him for like 2mnths (i was kind of wishing it wouldnt though it set him apart from my other 2 sens and i called him "gimpy" now i have to come up with another name )