Did you guys already talk about a theory that just came to me a while after my second viewing? Here goes:
Maybe Han isn't dead. Maybe everything that has happened around this point (around when Luke disappeared) was already seen by Luke or Leia as a vision of the future? Leia didn't seem very shocked when she felt Han get stabbed or when everyone made it back to base.
Also, it was like Han knew what was going to happen when he walked up to Ren. The way the scene played out to me seemed like Han helped Ren impale him with the lightsaber, because it was something they both knew had to happen according to plan. That's why Ren said "thank you". Now, I really have no idea how Han could survive the fall.
Maybe these events were destined to happen, Luke, Leia, Han, Maz, and even Ren knew that they had to play their part in all of this exactly as planned, and that there's a greater evil at play (beyond Snoke, possibly) that must be dealt with in the future.