We are going through the same in our company. What we do is Jamf lock the systems so they are unusable and ship them boxes and return labels.
I reached out to our legal department about holding back pay, but it is illegal because it is for work performed. What we did discover is that we could deduct the cost of the equipment from the paycheck, but we have not done that yet.
Currently, my team (IT) is FedEx-ing an empty laptop box and bubble wrap, tape, etc... To each employee. My employees and are keep stock of boxes and packing materials in our homes. What I would like to find to alleviate the workload to my team, is a site that we could order and ship directly to the user the packing materials. I know Fedex sells the laptop boxes in store, but does not ship it.