I don’t think the pubbies will impeach and try Rosenstein. But if they do, Chief Justice Roberts will be the judge in the Senate trial, and I suspect he might order all of the documents relevant to Rosenstein’s crimes, and the crimes of others he has been refusing to release, released to the Representatives and their legal team.
That would be a huge ouchie for Rosenstein and everyone in the Obama administration, all the way up to Obama and even President Jarrett.
If Rosenstein is impeached, that would create cover from Trump to fire him.