I would plan on having to have the besadmin reactivate it. I have heard that if you upgrade on a computer on the same network as the BES then it will reactivate itself. everytime I have upgraded I have had to reset my activation password on the BES.
I Had to get my BES re-activated for work e-mail to work after OS upgrade. Not sure how that could be avoided?
If your work PC has Desktop Manager loaded on it and you do the upgrade while plugged into that with access to the inside of the network that the BES server is on... no need to ask for password. It reactivates after the upgrade is done automatically.