I recommended deletion on this answer which the user then edited to improve his answer based on the review.
How can I recant that review and cancel the delete recommendation?
As Mark Kirby mentioned in a comment there is no way to change a review after you've done it. A Recommend deletion vote can't be retracted, and neither can a delete vote* cast by a user with delete vote privilege (I wish they could).
In a situation where a non-answer becomes an answer or for any other reason you change your mind about whether a post should be deleted, there are a few options:
If you improve the post, perhaps rephrasing a "me too" statement or question at the beginning, others may be less likely to vote to delete it. I am saying this with caution however, as I am unsure in what circumstances this may have the drastic effect of completing the review without any further scrutiny of the post. I had thought this only happened when editing was selected as an option in the queue, but it seems like any edit can have that effect. Therefore, I recommend doing this only if you are very sure the post should not be deleted.
This is annoying, because it's not very easy to keep track of posts. You could favourite the question, but you might forget to check back or forget why you favourited it (as I do). I usually just press the back button to the review and leave the browser tab open until the review completes, which usually takes less than 24 hours. If you have less than 10k reputation, you presumably won't be able to see the post if it has been deleted, but you'll probably see something like this which vaguely suggests that it has.
If the post is deleted but you think it shouldn't have been (or vice versa), you can
* three non-mod delete votes, which can only be cast on negatively scored answers (or zero scored answers through the queue), delete an answer, and three non-mod undelete votes, which can only be used if a mod did not delete the post, undelete it. For questions, the situation is a little different, but that seems out of the scope of this question. The main point of this note is to point out that it takes three users with => 20k to (un)delete an answer and even then it's a conditional privilege.