At many organizations, Senior Engineer is not the end of the IC track, not even close. For example:
... > Senior Engr. > Staff Engr. > Sr. Staff Engr. > Principal Engr. > Sr. Principal Engr. > Distinguished Engr.
... > Senior Engr. > Staff Engr. > Sr. Staff Engr. > Principal Engr. > Sr. Principal Engr. > Distinguished Engr.
Indeed you can become a senior fellow at Google, but you aren't expected to. You are however expected to hit senior at some point in your career. There's no requirement to grow further, so the bar for senior is high.