No, it is not possible to Unarchive a Phish.

Archiving is permanent, and will result in the Phish being stopped immediately, with no further emails being sent. 

However, those who have already received the phish will still be able to interact, and any 'clicks' will be recorded as normal. 

If you wish to publish a new version of the same Phish, you can do this by following the instructions in this article: How to Copy a Phishing Template in 'Archive' State