>Is there any way, aside from an external .com file, to issue a Ctrl+Alt+Del, or other reboot command on a DOS based machine running Clipper '87 ?

I don't remember if Clipper has a means of accessing Int 21h or not. If so, it would be quite possible to reboot (I don't recall what you feed the interrupt to do so, though; I'd have to dig some books out of boxes. :-) Other than that, there should be plenty of .com files sitting out on the 'net that you could call.