If upgraded to the pro plan when the code is exported will that remove any and all instances of anything relating to Webflow including all the w- classes?
No. Upgrading will not remove Webflow references from the code.
You can remove some of it easily.
Other parts are a little more difficult.
Will it remove the generator metatag?
<meta name="generator" content="Webflow">
no... but you can do that in a couple seconds.
What is not easily removed? The w- classes?
you can do a global replace for w-...
but you also need to check the css files and rename the js references.
it can be done... it's just a pia.
You can use the "find in files" option in Sublime Text and replace the string "webflow" with anything you want. Just target the main folder your site files are in and its a snap. Replacing the w-classes is just as easy. White labeling an entire Webflow site takes less then 5 minutes of almost automated work.
Even though you can re-export it.... Work from a copy... not the original (exported code).