Is it possible then to undelete o restore a deleted account? If possible how?

I don't think that's possible... I mean, after deleting an a/c, tu can create another a/c using the same mail id... But I don't think its possible to undelete an a/c

No. The person would have to start again with a new account. He o she could create a similar account name to make it easier for people to recognise him o her though.

No, I doubt it. They ask before tu borrar your account if you're sure is your account will be removed permanently.