Putting a game on a platform is a matter of accessibility. There's no control the devs would need to cede to put this on steam, and they could even keep selling it off of steam, a cut of the proceeds from sales on steam will go to valve. The only thing I'm consciously unaware of and not willing to search for right this second is whether or not they could opt out of promotional sales, which is an issue people have had in the past but may have already been addressed.
No out of touch board of executives is going to take over direction of the game simply because it went onto a very publicly accessible (to developers) platform.
I'm all for the developers making the decision based on any whim of theirs at all, even sheer apathy, I already have the game, but no aspect of the game's "character" is at risk. The vast majority of games on steam are independent and wholly unsubsidized by anyone but the customers.