Who does Howard save at the end of Skippy Dies? Is it Carl? Is Ruprecht still with Lori when the school burns down?

The questions you are asking are purposely left unanswered; however, I will try to explain as much as I can about what you are asking.  First, we are not told the exact student that Mr. Howard Fallon (the history teacher) saves.  Mr. Fallon simply “raced back into the burning building and rescued a trapped student.”  Yes, the student certainly could be Carl.  The importance of the happening is not the particular student, but that both he/she and Mr. Fallon are recovering and that Mr. Fallon has behaved heroically.  Next, we learn about the status of Ruprecht and Lori only at the end of the book and are not told about their exact status as the school burns down.  In an earlier chapter, we learn that Lori is singing into her cell phone on the night of the concert (to try an experimental performance) and Ruprecht is backstage.  The call is eventually dropped which we can assume is because the school is burning down at the time.  Later, Ruprecht shows up at Lori’s window and throws pebbles to get her attention.  This is when they begin talking.  Again, we are not told exactly when the school was burning down.  We learn that it has burned down from a Christmas bulletin talked about later.  The school could have been burning down when Lori was singing on the phone and Ruprecht was backstage.  The school could have been burning down when Ruprecht was en route to Lori’s house.  The school could have been burning down after Ruprecht already arrived at Lori’s house.  The reader cannot be sure; however, what is important is that both Ruprecht and Lori surive.