They indicated that the loading time will depend on the number of items you have. If they're handling each item as a separate transaction, it makes you wonder if some of them can fail, and what happens to the item.
I wouldn't worry too much. ZOS seemed worried enough that they'll make sure it goes right, or that they can fix whatever goes wrong. I might wait until Tuesday to mail any guild dues.
But no we are not supposed to loose anything.
That said things happen.....I seriously doubt anyone will come on later "where's all my stuff??!?!?!". Seems unlikely.
We Fight For Cyrodiil.
We fight for The Daggerfall Covenant.
We fight for The Aldmeri Dominion.
We fight for The Ebonheart Pact.
We fight for Tamriel!