re: Pros and cons of switching from onsite exchange to Office 365

This all depends on if your current archiving solution is compatible with O365, which ours is. We are required to keep all emails for 10 years (florida sunshine law). Currently if a user leaves we delete the account and keep their mailbox. I know this was a key factor we brought up when discussing archivig with our Microsoft rep, and O365 has an additional archiving solution/subscription. I would suggest contacting a Microsoft rep and slgetting more information, or utilizing a vendor you have a relationship with.