Here's how I solved the problem of needing a fall back for when/if the CDN goes down.
<script src="https://js.arcgis.com/3.16/"></script> <script> window.dojo || document.write('<script src="/js/3.16/init.js">\x3C/script>');</script>
It check to see if dojo has been loaded, which is essentially seeing if the js library has been loaded. If not, it loads the local version.
Good idea, I have this as a parameter in the app I can change through a db script, but that requires identifying the problem and applying a fix after the fact. This is a more robust way to do this seamlessly. But, I mean the CDN never goes down, right? Right?!
Ha ha, yeah never