In addition to the instances Jennifer Ellis mentions (Jennifer Ellis’ answer to Is Quora deleting answers?), answers will also get instadeleted for spamming. (Already pointed out in Joe Buettner’s answer to Is Quora deleting answers?)
I’ve just had one answer get trapped by the SpamBot because I got link-happy in the answer. It was clearly a bot action, and I know why it thought they were spam, though that wasn’t the intention. I removed the links, appealed, and got the answer restored.
There’s a lot about Quora Moderation that I vehemently dislike; but I agree with Jennifer that the deletion of answers is sparing, justifiable (reasons are given, so it’s closer to transparency than the norm), and appealable.
I’m answering the question as stated, though Joe Buettner pointed out OP was actually talking about collapsed answers.