f(x) may be coming back soon.
While fans had been worried about f(x) especially because of Amber's recent post, news from Luna may make fans feel a little better. During a live Q&A session, Luna responded that there were comeback preparations happening currently. While she didn't specify if it was for her own solo track or f(x), but she did address it to Me U's, which is the fanclub for the entire group - so hopefully it's for the entire group.
You can see it at 4:00 above, and hopefully fans can see f(x) soon.