I don't think they did. *mīnaz probably goes back to an earlier *meynos, but I don't know where that came from.
Last edit: 22:18, 28 May 2014
It could be related to the *-nos in *(h)óy(h)nos, and then the *mey- would be an e-grade of the PIE *moy. But I don't know how the *-nos suffix works, and it seems to be in free variation with *-kos and *-wos. Is it a known suffix?
As far as I know *-nos forms adjectives from verbal roots, but I'm not aware of any other use.
Could *éy- have been a verbal root besides a pronoun?