Pricing, timelines, ownership, reporting, international engagements, and how the work actually runs day to day.
Accounts are documented so knowledge does not live in one person head. You would be introduced to the replacement with a handover call rather than discovering the change through a different name in your inbox.
By going back to what the work is supposed to achieve. If we think a change will hurt results we will say so once, with reasoning. After that it is your brand and your decision, and we note it so we can judge the outcome fairly later.
Send it across. We reply within 24 hours and add good questions to this page.