Will Safari preserve my windows and tabs across an OS update?
I wouldn't count on it. Specifically, I had several machines not rejoin WiFi after the upgrade, so the tabs didn't load with no network. I would save all open tabs to an HTML document and save it just in case if you really can't afford to lose your workspace. 


http://brettterpstra.com/2015/09/04/share-browser-tabs-in-one-link/


Bookmarking is overkill and this tool will be useful going forward without needing to clean out your bookmarks after the update.