So far, HBO appears to be keeping most Game of Thrones fans as subscribers

Variety

Since the series finale was one month ago, it's still too early to tell how losing Game of Thrones will impact HBO. But early data from Senor Tower found that HBO "was able to hold onto 84% of the revenue from those new subscribers at the first billing cycle after the finale." HBO suffered much steeper drops in new subscribers after the finales for Seasons 5 and 6.