ROM flashing using Odin on Galaxy S4 interrupted. Odin is still running. Is there anything I can do?
After waiting a couple of days and not finding any answers, I restarted the device. It booted to a screen saying


  Firmware upgrade encountered an issue. Please select recovery mode in Kies &amp; try again.




I tried using recovery mode in Kies, but Kies gave me an error message saying that the device is not supported. However, I noticed that the text in the upper left corner of the screen indicated that the phone was in Odin mode (showing the above message instead of the usual Downloading...do not turn off target!!!). So, I launched the Odin desktop app and tried flashing the firmware again, and that worked.

Basically, I was lucky. In some cases if a ROM flash fails, you can't get back into Odin mode. So, I'm posting this in case it helps someone, but I'm not going to mark this as the accepted answer, because I'd like to see if anyone has a solution that avoids taking the risk of restarting and hoping for the best.