A 'Close Sidebar' menu entry should be added in the sidebar's menu (below 'Undock') that acts like the View->Sidebar toggle
This has been decided in the Design chat.
Samuel Mehrbrodt committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=5131750da6df95643e89127349b95df33be2feb4 fdo#85937 Add 'Close Sidebar' command to Sidebar menu It will be available in 4.5.0. The patch should be included in the daily builds available at http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: http://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.
Samuel Mehrbrodt committed a patch related to this issue. It has been pushed to "libreoffice-4-4": http://cgit.freedesktop.org/libreoffice/core/commit/?id=f0b969179d8583a98849b0b8df1e1f5f130b3fbf&h=libreoffice-4-4 fdo#85937 Add 'Close Sidebar' command to Sidebar menu It will be available in 4.4.0.0.beta2. The patch should be included in the daily builds available at http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: http://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.
This bug fix comes with LibreOffice 4.4 (release notes https://wiki.documentfoundation.org/ReleaseNotes/4.4) The sidebar drop down menu now has a 'Close Sidebar' entry.