Together with Korah - i. e., they were engulfed at the same time that Korah perished, for Korah himself appears to bare died among the two hundred and fifty incense offerers at the door of the tabernacle, not with Dathan and Abiram (compare Numbers 16:32 note).
Related Commentaries of Numbers 26:10
Numbers 26:10
10 And the earth opened her mouth, and swallowed them up together with Korah, when that company died, what time the fire devoured two hundred and fifty men: and they became a sign.