This came up again recently. To keep information centralized, we'll continue the discussion here.
Everything mentioned by rolfl here is still valid.
A similar situation has been reported on MSE ('15). There is an MSE FAQ on deletion too (How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion?), but it doesn't cover this situation explicitly. The paragraph 'How can I undelete one of my posts?' covers it in part, although it assumes it's the question asker who wants to put the undeleting process in gear:
If your post was deleted by high-reputation users or by the Community user, it will require three undelete votes to be undeleted (more if it's a question and it was popular) - politely asking for this on the per-site meta may attract the necessary votes if you make a good case for why the question should be restored (i.e. why the post doesn't meet the deletion criteria above).
The privileges/trusted-user help-center page states:
Trusted users are allowed to perform trusted actions, including:
- Voting to delete answers with score of -1 or lower
- Voting to undelete answers except those deleted by a moderator
- Voting to delete questions with a score of -3 or lower immediately after they are closed
- Editing tag wikis without needing approval
Emphasis mine. It doesn't say you can vote to undelete questions as well, but you can. More on that here and here.
Users self-deleting questions within minutes of receiving an answer is in some cases a form of vandalism, an abuse of the site.
The community is allowed to undelete questions as part of their content curating responsibility. Even though there will always be exceptions, I would encourage it in situations like these. Find users on meta or in chat to discuss a specific question and gather the required undelete votes if need be. Moderators can help out, but this shouldn't be necessary and we'll be very hesitant to put in the first vote. Content curation like this is something the community should be able to handle itself.