Metal extraction by pyrolysis
The answer appears to be forthcoming in the wikipedia article on silicon monoxide and references therein — to quote:


  $\ce{(SiO)_{n}}$ irreversibly disproportionates into $\ce{SiO2}$ and $\ce{Si}$ in a few hours between 400 and 800 °C and very rapidly between 1000 and 1440 °C, although the reaction does not go to completion.


The article implies that $\ce{(SiO)_{n}}$ generates a passivating layer of $\ce{SiO2}$ in contact with dioxygen, so presumably the slag would be encapsulated in a thin layer of that.

Additionally, silicon is not generally considered to be a metal, but rather a semimetal or metalloid.