Always difficult when headcount reduction is involved. Some thoughts:
– try to identify key persons upfront
– think of actions how to keep them onboard
– these actions could be financial (incentive, depending on integration success, only paid when still onboard after X months,…) or non financial (certain position, etc.)
– I think 1 on 1 sessions might be helpful for this, also to understand how they are in the process
– Maybe they think/know already that they will leave, always better to know this asap so you can detail out a plan B
I would implement the above mentioned actions in parallel with the start of the “official process and procedure”, where you draft Target Operating Models, define Org Charts, etc, but already having a view on the listed bullets above should give more comfort