Once an update to a message has been saved, unfortunately, it is not possible to revert to a previous saved version of that message.
The support team at Mixpanel recommends updating messages with caution, as support does not have a record of modifications made to messages. As a friendly reminder, by default anyone you add to your project has the ability to create and edit marketing communications (like messages), unless your plan enables you with permissioning.
Message editing tips
Though reverting to a previous saved version of a message is not possible, here are some tips and tricks for avoiding losing old messages copy:
Keep a change log of your messages copy outside of Mixpanel, like for example in a shared document where everyone can contribute to the text.
When editing messages, add a new variant instead of overwriting old text. That way, you can view analytics for each version of your message and keep a copy of the older message text for reference.
If that previous version was an email and was already sent to your users, you can check the reply-to address for any replies that also might contain the text of the previous version of the email.
If you had sent a test message of the previous version to yourself or a test account, you may keep old copy that way.