my DnD group needs a ruling: Can Sending be used to talk to a dead family member? If Speak with Dead is unavailable. That’s up to the DM. I myself would allow you to cast it and speak to them…but you probably won’t get a response, nor know if they heard.
— Matthew Mercer (@matthewmercer) December 21, 2018
Considering the dead join another plane of existence and Sending can cross that threshold opf interplanar communication, by the rules of the book I’d say yes. However of course if their soul was trapped, consumed, or destroyed, that changes things. If you and your late father are Goblins, and a Barghest devoured him, you’re probably not going to get a response from that shapeshifter’s stomach.