The items you had on your character during a Gear Update are sent to your mail, if you do not retrieve them in the allotted time, yes, they could be deleted when that mail is purged.
Had you used the Gear Update option previously or was this your first time? If this was your first time then no, it is unlikely that the process deleted your item.
The Tabard is part of your Transmogrification Collection. There was an update earlier this year that cleaned up several tabards, removing the physical item. I don’t think this is one of those, but it is part of your collection so you can still use the appearance. We’re unable to restore the physical item for this one.
For Shadowmourne, assuming we can verify that you completed the quest, which should be easy enough as I can see you completed the quest, we should be able to help restore it.
It does look like you have submit a few tickets on this and it seems the Game Masters might not have been aware of those facts. You have another open, I’ve tied the proper article to the ticket so they should be able to reference that.