Leaving without the migration stalling
Migrations rarely fail for technical reasons. They stall half-finished, people quietly go back to what works, and you end up paying for both.
The three things that actually break
Mail stops being delivered because the sending records were not moved properly. Calendar invites from outside stop matching. Somebody’s shared drive does not come across. All three are predictable, and all three are handled before the cutover rather than after.
Your staff do not run the migration
I move the data. They get a working account on a Monday and a page telling them what changed. Nobody is asked to export their own mailbox in their own time, which is how the last one stalled.
The old account stays alive until you say otherwise
We cut over with the previous provider still running behind us. If anything is wrong, you are back on it the same hour. You cancel it when you are satisfied, not before.
It replaces your provider rather than adding to it — the licence bill and the IT contract are the budget this comes out of.
Ask what your migration looks like