Well, I may as well join the party. iPad 2 owner here, have been using it for almost 4 years. Like so many others who use POP/SMTP for their email (comcast.net in my case), I've discovered that previously downloaded email on my iPad that are more than a couple of days old still show a Subject, but are now missing the body, attachments, etc. and replaced with "This message has not been downloaded from the server." Hundreds of them dating back to early 2012.
Note I use Outlook 2010 on my Windows 7 PC to send/receive email, and more importantly, to serve as a permanent storage location for ALL email (versus on Comcast's mail server somewhere). Therefore, for each of my email accounts in Outlook, I long ago deliberately chosen NOT to "Leave a copy of messages on the server". So, for me, I may have now forever lost the ability to view these older emails on my iPad (except for the Subject), at least I DO have full, permanent copies of everything on my PC's hard drive (mailbox.pst file, which I routinely back up).
I'm still amazed that the body of all email messages (& attachments) that were on my iPad were actually deleted when I updated iOS from 8.4 to 9.x. Absolutely incredible! I also find it amusing that some posts in this (and other) threads on the topic suggest that turning ON the option to "Leave a copy of messages on the server" is a solution, as if having it OFF in the first place is an error or mistake on my part. I don't WANT them left on the server and never have, nor should I have to do so in order to see email that has already been downloaded to the iPad!
Anyway, I too hope this problem is corrected in iOS 9.2 so that you're not forced to leave email on your server AND maintain a constant internet connection just to read email, but ... for those of you thinking that once (if?) the problem is corrected you'll have your old email/attachments, back ... sorry, but I'm afraid it's probably gone, permanently, from your iDevice. Ref. Settings/General/Storage & iCloud Usage/Manage Storage/Mail and you'll see just how much has been pruned by the iOS 9 update.