You could use my Close Excess Windows script, posted
here, and bind it to a button on the toolbar (see View->Customize Toolbar). If you can convince your fingers to click on that button (which you could place underneath the standard close button), it would prevent you from inadvertently closing the last window. I doubt Omni is going to tinker with the code at all before they issue a proper fix for the problem, but that might be a while yet, especially if you don't want to run alpha/beta test software.