I have done that in the past, but there is an upside to not doing it that way. If you use a CDN, and the user has already loaded it from the CDN via another site, that's only less thing to download. So it can make your site seem faster for a subset of users.
That might be doable if the library is jquery or whatever, but how are you going to replace google maps? Hosting an OSM tiles server is non-trivial, and I highly doubt that you'll be able to host it with better reliability than google.
jQuery isn't Google Maps. Different tools have different solutions.
You can save your site by self-hosting jQuery, but if your business depends on Google Maps you should at least handle failure more gracefully than a blank screen.
