One is that Leia will not survive the prologue having died following the birth of her child(ren) as either a prisoner of the remains of the Empire, or in the crashed Star Destroyer on Jakku. Meaning she's been dead for years and only seen in flashbacks or background informational story material (like the bits in Star Trek (2009) dealing with USS Kelvin, or Kirk and Spock as kids until we get to the "present")
Han Solo dying is also possible to hand over the Falcon to the next generation. I'd rather he live, because Han Solo is a fun character.
The only one that probably needs to live on is Luke, and only because someone has to teach these kids about the Force.