Charles Ellicott Commentary Numbers 26:10

"and the earth opened its 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." — Numbers 26:10 (ASV)

And the earth opened her mouth, and swallowed them up together with Korah ... — Hebrew, and Korah. It would appear from this verse that Korah perished in the earthquake with Dathan and Abiram.

The Samaritan Pentateuch, however, has a different reading here. It transposes the words "and Korah," and combines them with the words "and the two hundred and fifty men": thus—when the fire devoured Korah and the two hundred and fifty men. (See Notes on Numbers 16:32; Numbers 16:35).

It is possible that there may have been an omission here of the words which are found in Numbers 16:32, all the men that pertained to, or of words denoting all the goods belonging to.