ST already create an empty view ready to use in most case (New Window, Close Project, ...), so the only case I see is when you manually close all files, which I probably never do.
What's your workflow that result an empty ST window ?
In addition, hitting ctrl+n before pasting is not a big deal...
And you can always use a plugin to do what you want (not tested):
import sublime, sublime_plugin
if not self.window.views():