We do this with all of our PHP dependencies at work, they get committed into the project. The upside is that the deployment process is simpler, the server doesn't have to fetch all the libraries you depend on within each deploy and it mitigates all of the risk of left-pad style bullshit.
You can store dependencies in version control so you can continue working when there is problem with remote package manager repositories as you just checkout last working version with all dependencies from git.
Store all of your dependencies locally.
If something disappears then at least you can continue until you find a replacement.