how to retrive things that disappear in upgrades

[menthols72]

how to finds things that wear deleted or miss placed

[Lindal Kidd]

A viewer upgrade does not delete or move inventory items, with the possible exception of changes to the content of your Library folder.  

If things are missing from your inventory, try a manual cache clear, following the instructions here: http://wiki.phoenixviewer.com/fs_cache_clear

[Rolig Loon]

If you are concerned about things that might go missing during a region's server maintenance or upgrade (rather than your viewer's upgrade), you may be out of luck.  Linden Lab is always careful to remind people when they are about to do routine maintenance, and they always say, "Please refrain from rezzing no-copy objects and making in world L$ transactions, and remember to save all builds."  The reason they say that is that sometimes it's necessary to do a rollback to reset a region to a previous state while they work on it.  If your no-copy items or new builds didn't exist during that previous state, they will be lost forever.  Unfortunately, the same is true during unplanned maintenance like the work they had to do over last weekend.  You have no warning then, because they are responding to an unexpected emergency.