Your IT department will be busy during a divestiture.
The obvious part your IT department will play is data extraction for the data that needs to moved (or copied) from the current company to the divested company. All of your interfaces need to be reviewed to determine which of those need to be turned off or adjusted to prevent data from the divested company coming into your system after the divestiture is complete.
When considering a divestiture there are many considerations. Some of these are:
How much history needs to remain on the current books?
How much history needs to be extracted for the divested company?
Coordination between IT departments (current company, divested organization) on current interfaces and how they will be handled in the divested organization.
Make sure to start with a BRD – Business Requirement Document – so you have a road map of what is expected throughout the process. This helps you, the divested parties and your partner know what is expected from all parties.