Removable batteries would have done nothing to improve this situation (being banned on planes). Once a phone model has been recalled for potential battery fires, the entire model is tainted. The TSA or airlines would have no way of knowing by looking at the phone if the battery is affected or not. If they simply could send replacement batteries to affected users, or swap them right in the store because of a removable battery, there could still be potentially thousands of affected batteries out in the wild.
To the contrary, I could see where removable batteries would make the risk of a ban even worse. Suppose Samsung had made the battery user-swappable, and Samsung's batteries didn't have an issue. But a batch of cheap batteries for the model goes up for sale on Amazon/eBay, and suddenly reports of fires start to crop up. Even once the cause of the fires is identified as cheap, aftermarket batteries, airlines could ban the entire phone model because of the risk that users may have replaced the original battery with a cheap knock-off.
Surely, a easily swapped battery might have saved Samsung money in this case by allowing for an easy field replacement of a defective battery, but it wouldn't have saved the Note 7 line from being tainted.