Enonic version: Enonic XP 6.3
Is it possible to undo delete so that “pending delete” is removed from the admin interface?
Not yet I’m afraid. With 6.6 (4 weeks) you will be able to instantly delete published items (skipping the pending delete state), and for 6.7 we will provide an “cancel delete” operation, that aborts a pending delete state.
Ok!
Somebody has clicked “delete” on the full site tree; thus if somebody now clicks “Publish”, they will delete the full site.
What should we do?
I see 
The delete status is a flag in the draft branch metadata. I guess a script that resets this attribute could be created - or you could do a restore if it is very urgent!
BTW: We have added extra protection against such errors in 6.6. - where you must write a confirmation number when deleting sites.
Ok, I’ll submit a support request.