Thanks.
Yes, that sounds like a half-the-packages-installed kind of update situation.
I’d hop into the terminal (or rather, ssh) and first try to find out what’s breaking pkcon (very likely the broken part is packagekitd, or dbus itself).
There may be useful packages left at /home/.pk-zypp-dist-upgrade-cache.
If that can be made to work again, something like sfos-upgrade --verify, or very careful use of zypper dup might be able to recover the install/update.
You can also try to look through /var/log/zypp/history and try to find which installation failed, if any.
This story tells about how someone could recover this way from a broken update.