I'd just like to chime in with this good ol' article. That pretty much paints the picture that, yes. If you want a second season of your anime, you'd have to buy the blu-rays.

http://goboiano.com/list/5373-anime-producer-explains-why-second-seasons-don%2527t-happen

Now of course, there's probably some other interesting ideas other than that. For example, Light Novel second seasons are more likely to happen due to good sales of Light novels. Though maybe Sam could pitch in. I'm not sure how well Konosuba sold blu-ray wise, but it did increase the sales of the novel by threefolds.