Setting a property status to "Under Offer" will not remove the record from the website. It simply adds an "Under Offer" icon on the results page and adds "Under Offer" to the Tenure Type on the property details page.
For Example:
Depending on your CRM system, if you would like to remove the property then you will need to mark as sold/archive/delete or whichever the system option is. If you're unsure then please speak with your feed provider.