Maybe timestamping likes could solve this problem? I don’t know if this information is currently even stired in the database, but if it is, it could be made available to users, perhaps next to the username that appears on mouse over the avatar of the user who liked the post.
Or wait, we don’t even need that much information. It would suffice to store which revision of the post was liked (and as long as it is the current revision, that information would also be hidden).
I have no idea how difficult this is to implement, but I’d like to say that this would be useful also in less extreme cases that the one in the OP. I do remember returning to a post I originally liked and noticing that it had been edited - not a lot, but sufficiently to make me withdraw my like. If users could have seen that it was the original version on the post that I liked, I would not have withdrawn it. Most importantly, though, it was only by chance that I noticed the change.
Another possibility might be to allow users to receive notifications on edits for posts that they have liked. But that sounds like a bigger project…