Yes. In many cases, switching to the new version of the package is nothing more than rewriting a symlink. Sometimes it's more involved, like restarting a service. Either way, the cut over happens after building the new package has completed successfully. If building the package fails, it has no effect on the running system.
I suppose there is still a window in which an error could leave the system in an inconsistent state, but it's pretty narrow, and the error would have to be a kernel panic or something like that.
I suppose there is still a window in which an error could leave the system in an inconsistent state, but it's pretty narrow, and the error would have to be a kernel panic or something like that.