Or HaChaim on Numbers 26:11/אור החיים על במדבר כ״ו:י״א

1 ובני קרח לא מתו. However, Korach's sons had not died. It is somewhat surprising that the Torah informs us about this fact here instead of in the story about Korach or in connection with the count of the Levites where we should have been told about which Levites had died. If you accept what we have written it is evident that the Torah chose this occasion to reveal who was the root-cause of Korach's uprising, i.e. Datan and Aviram. If so this was the place to inform us about some other redeeming quality of Korach, namely that his sons were righteous and did not join their father in his rebellion or that they retracted in time. At any rate, whereas Datan and Aviram and all their "houses," i.e. their offspring perished, Korach's sons did not. This is another factor which supports the theory that Datan and Aviram had been the instigators all along.