My understanding is that if you're using just plain vue.js (without any tools or npm magic), you're not gonna be able to use single file components.
You can "do without them" but going to .vue files that you like, and splitting them back up into their HTML and JS bits and copying and pasting them into places you like.
vue really isn't at its full potential without using webpack/browsify. But I understand not wanting to use it.
For example, we've been sprinkling vue into an existing jquery+bootstrap internal application. It's flask/python, so we just went in and split up things that would be a .vue component into HTML snippets that we can embed using our templating engine, and JS components that you just src include. Now we have bare bones reusuability (no composability though). We'll probably have to swallow the bullet and just figure out webpack/browsify.