I got a WC female that I bought after she dropped her eggs - she took a couple of rat pups and then went off feed for 18 months - that whole time she lost around 125 grams.

Other than that I can think of only one that went about a year for no apparent reason - I cold be wrong I haven't always kept the best of feed records - but for the most part 8-9 months is around the max that some of mine have gone off for their winter fast.