In a class he gave in the 90s, Rabbi Prof. Shnayer Leiman said that he believes that once all of the fragments of the Dead Sea Scrolls are properly analyzed and made public, it is very likely that the verse "אם תעזבנו יום יומים אעזבך - If thou forgettest Me one day, I will forget thee two days", which the Yerushalmi and the Sifrei quote in the name of a text called "Megillat Chasssidim", will be found among the fragments (9:28-10:45).
Does anyone know whether it was indeed found?