If it's a stand and deliver give the shooters the option. I have witnessed, issued and received too many penalties for not reholstering when pistols start from a non muscle memory position. The only time I would make it mandatory to reholster the pistols when they start on a table is if there will be a safety issue such as down range movement. Makes no difference on this stage, unless the stage writer likes the idea of mandatory reholster for some reason.