Okay, I'd done with whatever Internet Exlorer replacement that Windows 10 uses. I go out to run and when I come back, it has eliminated all my tabs. And there is no apparent way to open closed tabs.
If it wasn't for the large number of bookmarks I have committed to IE, I'd just switch to Firefox which seems to survive these periodic purges.
But if I get a fourth purge while using the latest IE that is loading now, I'll eat the sunk costs and rebuild in Firefox.