I played a couple with that concept.
I like how you did it, with the drag and drop and feedback on the mission.
I would like a mecanic where you are not obligated to send them all to their doom.
Maybe you could have one mission at a time and you decide if you send someone on it or not.
Then you would have a returning timer (x day, week or years), maybe you could see a thumbnail of the heroes away, with health bar. and you could send help or maybe you could send multiple heroes to the same mission.
Your game has a lot of potential, it's nicely wrap, with all this text.
Good job!