When a tab is deleted, there is no record of it in the Conversation view that I can tell. I am looking through the Office 365 audit logs, but it doesn't seem to track tab changes in for the Teams component that I can tell.
Ahhh.. I found it. The first time I went to the Teams section it was only showing 9 options, now I see all 19.
The audit log though is a bit obscure. The name of the tab isn't in it. You can see the user email, the team and channel name, but that's it. Everything else is just a bunch of GUIDs. Ok if you know what you are specifically looking for. Not so much if there are 10 deletions and you are trying to figure out who did which one's.