Well, it's now another 24 hours later for me (here in Australia) and so far, everything looks to be working as I expect it would. I will keep you posted over the next few days
Just for your information, for my testing, I downloaded everything to my iPad and iPhone, both of which are set to leave the message on the server. Then I downloaded everything to my iMac which I have reset to delete messages from the server. If I then look at my iPad and iPhone, everything is still there, in all folders - Inbox, Sent & Rubbish, both with and without Airplane mode engaged. So, I am very encouraged. Note too that I am only working with post 9.2 emails; everything before then could be polluted in one way another so the only fair way to test the update, is with post update material.
None on this excuses Apples arrogant, unconscionable conduct in allowing their customers to suffer in the way they have. The bug should never have made it through to 9.0, and at the very least, should have been dealt with promptly in 9.1. To have allowed it to drag on for so long, doing the physical and emotional damage it did, is border line criminal.