What if Zeke has switched sides already? Maybe that’s why the guard (who I suspect to be Connie) told him to go another direction.
I think Falco and Gabi will be the two survivors because Reiner will most likely want his cousin and possible Armored Titan successor to be safe.
Magath might know about Eren (and possibly two to three more scouts) being in Marley and working with Zeke. He hasn’t done anything because he might also have doubts about what Billy is saying about Eren and is not sure which side to be on or he thinks that Zeke can handle them.
You are right, chapter 100 is going to be gold.