/usr/bin/open executable disappeared I am on macOS High Sierra (Version 10.13.3) all recent updates are installed.
The open executable is not in the /usr/bin folder anymore.

Is there anyway to repair the system so that I can get it again?
I have no clue how this happened in the first place, maybe after the last macOS update. Did I miss something in their release notes? 

To clarify, this is not a path issue, the executable just is not there anymore.
Since SIP was disabled there is a high chance this was a user error on my side like the comments suggested. I did not want to do a complete reinstall due to all the hassle that would ensue.

This problem ended up getting fixed by itself when the next macOS update was released. After installing the update the open executable was back at its original place.

Hope this helps people encountering a similar issue.