Indigos like shrubby growth, so if you have recently cleaned up your yard they may have taken flight for shrubbier areas. To be honest I am not sure how long they stay, I think it is in line with the seasons so when the summer gets too hot they will head back up north to their southern canadian providences. So you should see him again, just remember to leave part of your yard a little shrubby and weedy and leave out some nyjer seed for him which they love. I am so happy you got to see one. I was thrilled the other day because I saw my first yellow warbler. Additionally he's probably in the mid cycle of his migration, so he probably started his migration back in November and as the weather heats up, he will be heading back up to the lower parts of Canada where he originally came from if you are in the eastern part of the United States.