My wife avers that portals take damage if a portal they they are linked to is destroyed. I haven't found anything about this and keep telling her that the "damage" she's seeing on these portals is actually just normal resonator decay. Who's right? (Other than my wife, who is always right.)
Yes and No.
The only way in which a linked-to portal is damaged is through link mitigation. A portal gains mitigation (defense) directly related to the number of incoming and outgoing links it has, up to 10. So while the resonators on the linked-to portal do not suffer any damage themselves, they become more vulnerable to others attacking.