Restart Safari and reopen all windows and tabs from previous session.

gistfile1.js

function run() {
	// Quit
	var safari = Application('Safari');
	safari.activate();
	safari.quit()

	// Reopen safari
	safari.activate();

	// Get menu
	var se = Application('System Events');
	var proc = se.processes.byName('Safari');
	var logMenu = proc.menuBars[0].menuBarItems[5];

	// Reopen from last session
	// Replace string with whatever "Open all windows from previous session" is in your language
	logMenu.menus[0].menuItems.byName('Åpne alle vinduer fra forrige økt på nytt').click();
}