It depends on a couple of things.
Firstly your storage, if you're using a WORM device (such as a JukeBox) then you cannot delete items, if you use a compliance device with compliance enabled and a retention to keep it for ever (such as a NetApp with SnapLock enabled or a Centera in Governance mode) then you cannot delete the items per the retention.
If you have Collections enabled, you can do a deletion of an item, however the core files stored in Enterprise Vault will remain until a process called "Sparse Collections" kicks in, and can take months for it to run and delete that data (could even take years theoretically)
Also if you have the "Dumpster" enabled, Enterprise Vault will keep a hold of the item for up to 14 days (set by default) so that users can get the data back OK, but you can disable it if need be.
Also items will remain on backup, but theres not much you can do about that, but in a disaster recovery scenario you might end up restoring the items and placing them back in to the Vault Stores and Indexes, and users or storage expiry will need to delete those items again.
One other thing as well if you use Discovery Accelerator , you could place an item on Legal Hold, meaning that the user cannot delete the items, and neither will storage expiry delete them or if you delete the users archive, the item will not be deleted..... But this is by design because they are on legal hold and must not be deleted.
As for a trail, you will have an entry for the item for about 42 days in a table called journal delete, but it won't give you much information about the item, with some effort you could determine which user the item belongs to, what folder it was in, and what the sent date and the archived date was, but you wouldn't be able to judge content, who it was sent to/from or anything about its attachments.
So really, as long as you are on a regular NTFS/CIFS drive without Collections, you should be able to delete with confidence :)
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