Thanks, George. I had the same problem with the missing "END:VEVENT". When I double clicked the filename to add it to Calendar an error message window popped up but it disappeared in less than a second, and I could never read what it said ("SAD"). However, your solution solved my problem.
M.Y.1 said he/she solved the problem by following the link from the confirmation email and then clicked to add the iCal event. What link in the confirmation email? The only links I found from the confirmation email were ones that led to my Flight Information page for my confirmation number, and that's the page that has the button that creates the incorrect iCal .ics file with the missing "END:VEVENT".
I also discovered a bug in an iCal event created by my hotel reservation on that same trip. When I double clicked the .ics file to add it to my calendar, it failed and the error message was "missing end date" (and, that popup didn't instantly disappear). But, there was both a "DTSTART:" and "DTEND:" line in the .ics file. However, when I compared the .ics file for Delta and the .ics file for the hotel I noticed the hotel's .ics file inserted a blank between "DTSTART:" and the date value, same for "DTEND:", but the Delta .ics file had no blank. I deleted the blank in the "DTSTART:" and "DTEND:" lines, then double clicked again on the file name, and it loaded correctly. To me (as a retired university professor of Computer Science) that seems like sloppy software design by Apple's iCal developers rather than a bug in the hotel's event creation software. I.e., Apple iCal developers should have written their software to ignore blank space between the tag and its value, IMO.