Debian 8 Linode has lost all networking connectivity after installing package dependencies for imapsync

After looking into this, I wasn't able to find any specific references to losing all network connectivity. It seems that imapsync can have installation issues related to packages, I'd recommend Fixing Broken Packages and also potentially retracing your Installation Steps

It may also be useful to try and replicate this on a different OS, such as Ubuntu 18.04, and see if the same issues are arising. Hopefully someone else here has more experience with this, you could also reach out to imapsync yourself as this could be a bug.