[Edit: looks like the question is now undeleted; the principle of what should be okay remains]
Those of you without the privilege to see deleted questions won't get anything out of the link, but here is a question that was posted 11 days ago.
Since it had sat there unanswered for a week and a half without any response, I gave a fairly lengthy partial answer yesterday-ish (depending on your time zone it may be 2 days ago), with some explanations of where further clarification would be required for a more complete answer (which explanations were much too long for a comment -- or even two comments)
The OP's response was to delete the question, which of course wasted the effort I had put into responding to the question.
I find something like this happens ... well not especially often, but it's not all that rare either, and it seems to be happening more frequently.
At least partly as a result of events like this, I find I'm less likely to actually post an answer a question from a low-reputation user than I would have been say a year ago.
My answering rate is down to below half what it was say last January -- and of course there are a number of reasons why that would happen -- but this perception of the increasing risk of wasting my time is certainly a contributing factor.
I have on one previous occasion undeleted a post where the OP deleted pretty much as soon as I answered, but that (undeleting it myself) is not something I'd seek to do as a matter of course in relation to posts I'd put an answer on (I'd do it with someone else's answer though, as long as there was some value in the answer, since there's no danger of it being self-serving to do so then).
It looks like OPs can only delete a question with an answer if there's only one answer and the answer isn't upvoted ... but that simply seems to be encouraging OPs to delete as quickly as possible if they decide their question is no longer worth investing time to fix (rather than actually put in a little effort to fix it with an edit).
What's a reasonable response to this sort of thing?
Should I just accept that I should exercise more caution and only answer questions I don't think the OP is likely to delete? If I'm not the only one that feels that way, our answer rate will presumably drop even more quickly than it has been.
Or should I post more low-effort answers, only investing more effort where the OP doesn't see fit to abandon ship at the first sign of difficulty?
Or should I seek some assurance the OP won't delete as soon as I post a substantial answer?
I really don't know what to do, but I'm getting quite cheesed off at the cavalier way answers can be just trashed because the OP feels like it.
[Edit 23Jan: I realize in retrospect the correct response to the question by the StackExchange model would have been simply to comment pointing out the biggest issues with the question and simply put the question on hold until it was improved, or eventually, to delete it if it was not e.g. see the discussion here as it relates to borderline questions. To quote from the link "rather a few borderline posts be deleted than the site be overwhelmed with garbage". So I probably did the wrong thing in trying to partially answer it at all.]