Depends on what they actually got. Names and email addresses? Considered public and are not so valuable. Universities usually publish those in a directory anyway.
Messages between students and instructors? Likely pretty boring, but possibly embarassing or confidential for a given individual.
Grades? Could be a FERPA violation.
Critical PII such as SSNs? Probably not in the LMS to begin with.
I have trouble imagining that a ransomware group would care about a regulation like FERPA when they've already done something criminal that would more than enough for prosecution if they got caught.
I just spoke with a K-12 teacher I know, and she confirmed SSNs in the Canvas instance.
Yikes.
SSNs have been used as student IDs by particularly stupid educational institutions. The 'nice' thing about getting SSNs from students is the likelihood they'll live for a long time after the breach and thus be subject to identity theft for many years to come.