Iv been pondering over this for several days, if he prayed Witr without making Shafa this is because of his previous "Salafi" or other Schools inclination then i don't see why he should repeat his Salah, it is like saying a Shafi'i prayed Witr like that for 3 years and felt he wanted to become a Hanafi and when he did become a Hanafi it would mean his three years of Witr would have to be repeated, that is very severe. Yes a Hanafi shouldn't pray like that, but clearly the brother in question (due to his constant Fiqhi question on Ikthilaf issues) wasn't a Hanafi previously, or didn't know what he was.
Iv never heard a Fatwa from any Mufti that a previous Salafi who has become Hanafi has to repeat his Salat al-Witr, yes i have heard those prayers that were prayed with Masah over normal socks needed to be repeated but never Salat al-Witr. (if there is i would like to see it)
This issue needs to be thought through by a Mufti.