Will Safari preserve my windows and tabs across an OS update? I have a(n embarrassingly) large number of windows and tabs open in Safari on Mavericks right now, which I'd like to save, and I'd also like to do an OS upgrade sometime this week.

I have "restore windows" turned on, and Safari re-opened them for me a couple of weeks ago when my Mac crashed and rebooted.

Can I be confident that the same will happen after installing El Capitan? If not automatically, is there a cache file or folder I can save before the install/dig up afterwards to restore the windows? Should I just bookmark all the tabs?
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.