Survey after unsubscribe

I don't really think that's possible, your best bet is to redirect the user to such page on a third party website like surveymonkey.
would be good to have and info displayed on admin. so admins can check their clients.

all leading email service providers offer that on the unsubscribe confirm page and its a good way to know why the subs unsub. could be:

A. Receiving to many emails
B. Never signed up to that email list
C. Not interested to receive emails anymore

and results will show up on /backend under the customers account so ESP`s admins and support staff can troubleshoot.
another safety net for ESP to check if anyone on their ESP doesnt follow permission based email marketing strategies
@justme - That's actually an entirely different thing from what the op asked for.
What you purpose here, it has been discussed before i believe, it has greenlight :)