Hi Anne-Marie,
I had a 2 cm semicircular section of the side of my tongue removed almost 2 years ago. Today I have a small divot in the surgical area. It is maybe only 1/2 a centimeter.
I do think that the term regeneration may be inaccurate.
Aside from my personal experience, I can also draw from my observations as a dentist to answer your question. When a person has all of their teeth extracted and doesn't wear dentures, their tongue can get larger. Normally the teeth help to mantain the tongue's size. I have seen this many times but, it doesn't happen to everyone.
However, whatever you call it, the tongue can can enlarge, but there are limits to how much. With one sixth missing, I wouldn't expect it to all come back, but possibly some noticable difference may occur.
Hope this helps.
Jerry