The sulfide ion, S, does not exist in aqueous alkaline  solutions of NaS.  Instead sulfide converts to hydrosulfide:
:S +  HO  →  SH +  OH
Upon treatment with an acid, sulfide salts convert to hydrogen sulfide:
:S + H  →  SH
:SH + H  → HS
Oxidation of sulfide is a complicated process. Depending on the conditions, the oxidation can produce elemental sulfur, polysulfides, polythionates, sulfite, or sulfate. Metal sulfides react with halogens, forming sulfur and metal salts.
:8 MgS + 8 I → S + 8 MgI