Disposing equipment with PM's set up

Hello,

I am looking for guidance on best practice in relation to model pm's.  We are using JDE 9.0 and a tracking costs thru work orders on our fleet.  When we dispose of a piece of equipment in the master the allow work orders box is unchecked with will prevent new work orders from being created.  However, in order to maintain a clean system should the model pm's be deleted or left in the system after the equipment tied to the pm is disposed of. 

Thanks for your help.

Julie