In the end, Havelse probably did everything right. The year in the 3rd league was taken with them, but they didn’t put everything on the card for staying up in the league. So you will be able to start a new attempt next season in the regional league.
In the 3rd league, it now seems to be the norm that at least one climber goes down again straight away. After the introduction in 2008, there was only one climber in the first ten years who had to be relegated immediately (Elversberg 2014). In recent years there has always been exactly one relegated team in Cottbus (2019), Chemnitz (2020) and Lübeck (2021), with Cottbus and Chemnitz falling victim to the new relegation rule with four relegated teams.