I've came up with a list of things that would happen if Kingdom Hearts 3 was not profitable. I know this would never happen, so, in some random universe where it's not successful, here is what would happen.
1.Square Enix Bankruptcy
Square Enix has poured so much money into Kingdom Hearts 3 and Final Fantasy XV, combined with the moderate success of Final Fantasy XIII, Square is losing money, and fast. They have lost millions on the development of FFXV with it taking so long to be made. Back in the 80's, Square was developing a game called Holy Sword Legend for Famicom Disk System. The game was to span 6 disks and have a very long story. Square cancelled the project because it was going to be impossible to make and they had invested so much money into the project that Square almost went bankrupt, nothing to say that it won't happen again. They have invested so much money into both of these projects, if there not successful, Square Enix would eventually go bankrupt.
2.No More Kingdom Hearts
Like I said before, they have invested so much money into this game, but if they don't see the figures that they want to see for this game, then they will decide that the series id not profitable and forget about Kingdom Hearts all together. I know that the other games were profitable and made them a lot of money, but, again, with the money they put into this thing and FFXV, they are in a bad spot right now.
3.First Sign Video Games Are Dying Out
With a series like Kingdom Hearts, there are so many fans that are wanting this game come out. But if it's not profitable, Square would eventually go away. With them gone, RPG's won't be as common anymore and RPG's are arguably the 2nd biggest genre in gaming. And when FPS's go away, what will we go to. A lot of RPG company's would go away , which would cause a domino effect.
I hope you enjoyed reading my reasons for my thoughts on the subject and I hope I've changed your mindset on the situation.