chrome – Are saved passwords in browsers secure, when stored online?

As with pretty much everything that is managed by cloud providers, secrets management as a service is susceptible to hacking attacks, HOWEVER, I would trust Mozilla’s and Google’s secure secrets management capability and infrastructure security in general much more than keeping those secrets on tools running on my machine.

To your last question, all major cloud providers offer you the capability of complete deletion of sensitive information they store, and are legally bound to fulfil that obligation when you are using their products.