As an answer to the first question about erasing data. I believe that you will be able to delete files in exactly the same way as you are doing currently.
Of course these files will remain in the backup set because you would have backed them up before the final delete. This is exactly the same as currently happens with backups to any other medium. The file does not get deleted from the backup set unless you wipe out the medium on to which you are backing up.
Any company worth its salt will not be relying on hard drives to perform mission critical backups. Removable media, usually tape, would be used with rotating sets and one set stored off site in a secure place.
I don't see Time Machine being a Company wide backup system and would, in your scenario, not be turned on.
Just a thought
I was looking at the preview for the upcoming Leopard Release of Mac OS 10. And as a Windows user I have to say that I'm impressed especially by one application, Time Machine. However I have two questions. One if you intentially want to delete a file how would you be able to do that. Say for example that you work for a major corporation who is going to buy another comapny. Those are sensitive business files stored on your computer. Now lest say for some strange reason because of a security breach you needed to get rid of those files off of your Mac, how would you do it, with time machine enabled it doesn't seem possible because they would be backed up several times. I can never see a file ever truly being deleted, which could be a potential security risk.
Another question is what happens when the slave drive holding your backup (a.k.a. Time Machine) data fills to capacity. Does anybody have any specific information on these two questions. Thanks.