When Ryan Callahan is ready to rejoin the Rangers lineup, he will rejoin the lineup, and in a top-six role. There is no debate about that. And though there has been no official declaration, indications are the Rangers’ captain will return Friday night against the Penguins after having missed nine games with a sprained left MCL he sustained against Nashville on Dec. 10. That means coach Alain Vigneault will have to scratch one forward from the lineup that has gone 4-1 over the last five games while reconfiguring at least a couple of the line combinations that have been intact through the run that ended the calendar year. J.T. Miller is the most likely candidate to be scratched even though the 20-year-old has played his most consistent hockey of the season — if not of his brief, two-year-career — since going into the middle between Carl Hagelin and Benoit Pouliot five games ago to form a unit that has played up-tempo and has been reasonably effective below the hash marks. The Chris (Doesn’t Work Overtime) Kreider-Derek Stepan-Rick Nash putative top line is all but certain to remain intact, so Callahan would likely slide in on the right on the second line with Brad Richards in the middle and Mats Zuccarello on the left. That means Derek Brassard, who had been playing the left with Richards and Zuccarello (at RW), would return to his natural center position on the third line with Hagelin and Pouliot. Brassard hasn’t been especially effective at even-strength, and will never be mistaken for the prototypical third-line center, but he has excelled on the power play on what has become the first forward unit with Zuccarello and Pouliot. So he is not coming out of the lineup. Indeed, Brassard has assists on four of the Rangers’ five power-play goals over the last five games, with Pouliot scoring three times and Zuccarello contributing a goal and two assists. Brassard (4-9) and Zuccarello (3-10) are tied for the club lead with 13 power-play points while Pouliot leads with five goals.