Its tough to do much with these automatically, but you also can't ignore them..
Some autoresponders will have a "from" address from a central email administrative account, and embed the departed name in the body of the message. If you don't read the message you'll unsubscribe, delete or mark invalid the admin address, and continue to send messages to the invalid one.
Some messages include the name of the replacement in the message--might be a way to grow your database--but again, you have to read the message itself to figure that out.
It also makes sense to look through the normal out of office responses. You might find a few who have been "on vacation" for months (or years) and should be taken off the list.
The importance of this lies in the fact that some firms are turning their departed employee email addresses as spam traps. If you don't respond to repeated "so-and-so has left the company" messages and remove that name from your lists, you might be blocked at that firm..