Are there reasons to revoke my degree if I shared old notes with a current student who was caught plagiarizing my work?
I highly doubt that you will face any consequence more serious than being blacklisted from that university for future enrollment. You've already graduated; I'm sure they dislike you sharing answers with current students, but that hardly seems like justification to revoke a degree that you previously earned. If they do contact you about revoking a degree, lawyer up. Sharing answers to old homework problems does not seem like reasonable grounds for claiming that a degree was granted incorrectly.
On the other hand, your friend will probably face the standard consequences for plagiarism.