Did you read the first part of the sentence? If it sells poorly on PC, the cost of removing it would be very miniscule, causing no harm, probably. Since the amount of sales removed was very little.
It's only a "massive decline" if they decide to pull it when it sells well, which they're not gonna.
It's up to the fans to keep the series on PC.
Ok technically the next entry wouldn't have the massive decline in sales, the current one would and their release decisions and subsequent arrogant and entitled attitude is what will have caused that. Continuing or even furthering that decline due to being stubborn, entitled and boneheaded rather than correcting their mistakes and trying to actually please their fanbase to increase sales would still be idiotic though.