Outlook PST and Caching rules

Hi,

I was wondering what type of security i can have in terms of PST.

1) Can i disable the PST export feature when users use outlook locally?

2) Can i set up a policy that all email is only on the cloud, and hence canno tbe backed up??

The reason i ask is if a employee leaves, they can export business critical data with them.

Thanks guys really need this help!