Well a season 3 for a Ln adaptation is already rare, so a third season for a LN finished years ago is eeeeeextremely improbable to say the least.
The goal is usually to advertise for the original work and especially in case of a series to advertise to new released content after all. There's no new released content here.
I think there's far more chance that we get someday a Magdala (same author) adaptation sinc eit's still published, rather than a third season of S&w. Both would be fine with me though.