Breaking news! Access to the stable repository has been restored! Steps have been taken to ensure that upgrading is once again safe.
If you updated previously, and now your system is broken, you will have to follow the steps here to chroot
into your system from a live USB session and fix it manually. Depending on where in the upgrade it failed, doing the chroot
step may fail because executables are not where they are expected to be. To fix this, add links to them from the live session, for example with Bash:
sudo ln -srvf /target/usr/bin/bash /target/bin/bash
sudo ln -srvf /target/usr/bin/bash /target/bin/sh
It may be necessary to repeat this for multiple files before chrooting will succeed. Hop into Solus Support Matrix or post in this thread if it still doesn't work after this for more personalized instructions.
Once you have successfully chrooted into your system, running sudo eopkg upgrade should upgrade and fix your system.
A more detailed explanation of what happened will be posted at a later time, once everything has settled. Thank you for your patience and understanding during this event.