I really hope they continue for a second season for this; proberly in what happens during the Kyoto arc of the light novels and afterwards. If they do plan it I wonder if we will get more of actual animations and few of those still motions. As well as if they will stay with the 15 min or go forward with a 30 min air time.
As of right now there has been no announcement for a sequel from TRIGGER. Ninja Slayer From Animation seems to adapting the Neo-Saitama in Flames story arc (the first 4 novels but not every story). A sequel depends on a lot of factors, such as sales and how much this has boosted the franchise. The series has been selling pretty well in my opinion with its obviously low budget animation. The first blu-ray volume sold 1,667 copies and the second has sold 1,452. Most anime with sequels tend to happen with sales around 10,000+, but Ninja Slayer doesn't look like it cost much, so it's possible it'll be enough for TRIGGER to do more.