What I am trying to get you to see is the distinction between an individual person, considered as a single entity, and a group of people considered together as a single entity. We won't be able to understand Paul's point in Romans 11:11-14 if we fail to maintain that distinction.
Consider Romans 10:21 for instance.
But as for Israel He says, “All the day long I have stretched out My hands to a disobedient and obstinate people.”
Here Paul speaks of "Israel" in general terms, whereby he considers all of his kinsmen taken together as a single entity. The single entity known as "Israel" is a disobedient and obstinate people. Never mind that one might find individuals within that group, who are
not disobedient and obstinate. Paul's generalization is true for the most part. A review of the Biblical text will bear out his broad universal statement about "Israel." It is true that Israel is a disobedient and obstinate people.
Likewise when he asks, "they did not stumble so as to fall, did they?" once again his statement considers all of his kinsmen taken together as a single entity. While it is true that some of his kinsmen didn't stumble, it is also true that the entity known as "Israel" did stumble. She, the single entity, sentenced her messiah to die on a cross. And because of this, her transgression became riches for the Gentiles (taken together as a single entity.) And here also, Paul is using the term "Gentiles" to represent the entire group of Gentiles, taken together as a single entity. Never mind that only a fraction of them were willing to take advantage of those riches. These riches were available to all of them if they wanted it.
Paul's point is that the single entity known as "Israel", which is comprised of all of Paul's kinsmen taken as a whole and treated as a single entity -- THAT entity did not fall to it's destruction. Contrary to the opinion of WPM, God didn't transmogrify the church into Israel. The topic of Romans 11:11 is not the church universal, but the kinsmen of Paul considered as a single entity.