There is a tradition in קבלה that קרח was secretly righteous and will come back in the end times and rise up. (They are not clear exactly about what he will do).
I am wondering if part of what contributed to that view was potentially that (maybe?) He and his friends were not part of the Golden Calf.
Are there any sources on the matter?
We can extrapolate from Rashi on Shemos 32:20:
ויקח את־העגל אשר עשו וישרף באש ויטחן עד אשר־דק ויזר על־פני המים וישק את־בני ישראל
He took the calf that they had made and burned it; he ground it to powder and strewed it upon the water and so made the Israelites drink it.
Rashi:
וישק את בני ישראל. נתכון לבדקן כסוטות; שלש מיתות נדונו שם, אם יש עדים והתראה בסיף – כמשפט אנשי עיר הנדחת שהן מרבין – עדים בלא התראה במגפה, שנאמר ויגף ה' את העם, לא עדים ולא התראה בהדרוקן, שבדקום המים וצבו בטניהם (יומא ס"ו): וישק את בני ישראל
AND HE GAVE THE CHILDREN OF ISRAEL TO DRINK OF IT — He intended to put them to the test as faithless wives were tried (cf. Numbers 5:12—31) (Avodah Zarah 44a). Three different death-penalties were inflicted there: It there were witnesses to the act of idolatry and a legal warning had preceded the deed the offender was put to death by the sword (cf. vv. 27, 28) as was the regulation regarding the inhabitants of an apostate city (Deuteronomy 13:13—18) when there were many (as was the case here; a single idolator, however, was subject to the death by stoning; cf. Deuteronomy 17:2—5). If there were witnesses but there had been no caution, they were destroyed by the plague, as it is said, (v. 35) “And the Lord plagued the people”. In cases where there were neither witnesses nor warning they were punished by dropsy — for the water which Moses gave them to drink put them to the test and if they were guilty their bellies swelled (cf. Yoma 66b).
In this Rashi, everyone who worshipped the Calf was accounted for and suffered death. As others have pointed out, the Levites gathered around Moshe to kill those who needed that type of death; regardless of that point, though, we can extrapolate from Korach's life itself that he didn't worship.
