Upvote:2
Does permesso di soggiorno override the visa?
Yes it does, meaning your permission to stay expires when the permesso does.
While the visa is valid, you can use either that or the permesso to enter Italy, but after the visa expired, you must use the permesso.
If you want to stay for longer, you Need to apply for an Extension of the permesso
Upvote:3
This resource states that a person can stay in Italy until the expiration date of their permesso di soggiorno. This is one of the best documents I found in English but can't verify the credibility