My Dad, A long time IT Administrator for mainframes would tell me over and over your only as good as your last viable backup. I am religious about backups and copy's of data, especially with big moves like this.
And I second the notion that most if not any of your users do not fully understand what is going to happen. Add on top that almost all are convinced of the "Clouds" ability to retain your data indefinitely. And you have a recipe for disaster.
And you look like the hero too when / if they need that data.
So get a nice external USB 3.0 HDD and dump the data there and save it.