[MTVN]

According to this:

Prosecutors could decide to retry Dassey, now 26, but they would face enormous hurdles in doing so because the judge ruled Dassey’s confession was involuntary and that confession was the centerpiece of the state’s case against Dassey, who was 16 when Halbach was murdered (read a transcript here).

The State of Wisconsin could also appeal Duffin’s decision. If prosecutors decided to appeal and lost, the State would also then have to decide whether to retry Dassey absent the confession. If the state wins on appeal, there won’t be a retrial because the conviction would stand. Prosecutors have not yet said whether they plan to appeal or retry Dassey

So a retrial seems unlikely. Also seems like this has no impact on Steven really seeing as Brendan's confession wasn't used in his trial