Well, the timing may be coincidental, but think about it, Yahoo's algo is designed to punish sites in the SERPS who engage in link spam, so it seems logical that your Yahoo search traffic would drop after your links were identified as link spam in Yahoo! answers. But if your links were on-topic, then that's not really fair.
Looks like you just have a RSS site, with no original content. Doesn't surprise me that you got deindexed.
I agree. Rss feed sites don't get looked upon as great from an seo perspective. However, it comes in cycles, so wait for it to come back into index....unless this is the last straw.
This is really surprising, because i am also used to answer in yahoo and my site's traffic is steady from yahoo (infact its increasing but not much) but heard first time this kind of incident. -- Ashish