There is one other benefit to separating Han’s Death from the Hosnian Destruction, and it is that adventure movies just don’t do that. After a devastating setback or sacrifice, our heroes usually win the day, and a new viewer would expect this. With the separation, the viewer can be surprised by the one-two punch rather than lumping the two tragedies into one.

JEDIT: An alternate of the alternate: After the Starkiller fires but before the beam reaches the Hosnian system, the Oscillator immediately blows up, but everything is suffused in the red glow of the beam. Kylo and Rey’s fight is bathed in red light until she is forced to the edge of the cliff and contacts the Force, at which point the Hosnian system is destroyed. At that moment, there is a massive disturbance in the Force that Rey senses, and this drives her to aggressively defeat Kylo. In this scenario, no Leia reaction is needed since Rey can sense the disturbance herself.