First, the Oaths are not Agada. By definition, Halachah means when the Gemora tells you it is forbidden to do something, which this does. In fact, it says You may not do this, and if you do, you will die. That makes it Halachah. Thats the definition of Halachah. (Similarly, the Oath of Naaseh V’Nishmah is also used by Chazal as Halachah, as in Shevuah chal al Sehvuah etc.) The poskim cite the oaths as halacha, as I cited above. The Oaths are brought down l’halachah in Rishonim and Achronim as viable and very real.
And secondly, there is no such thing as “just” an aggadic passage. Aggadah informs our religious outlook and cannot be ignored. Rabbeinu Tam writes that you DO pasken from Agadita unless it is against Halachah. Third, even if it is not Halachah, it still represents the Ratzon Hashem, meaning, negation of Halachah would merely relinquish us of any obligations in regard to making a State. But the Gemora clearly says that doing so will cause the deaths of Jews, like animals in the field. Even if that does not create any Halachic obligations, it surely tells us that the State is against the will of Hashem and that its existence causes deaths of Jews.
The Rambam in Igeres Taimon warns the Jews not to violate the Oaths, or else. He writes there that the Jews are suffering an evil, persecuting government that commits atrocities and wars against the Jews, and therefore the Jews should watch out not to violate the Oath by rebelling against them. It’s clear that even though the Goyim violate their Oath we cannot violate ours. The Medrash Aichah says clearly that the Romans violated their Oath, yet the generation of Bar Kochba was punished Chazal say because they violated the Oaths. The Maharal writes that even if the Goyim force us with torturous death to violate the Oath, we should rather submit to torturous death than violate them. The Oath that G-d gave us not to rebel against the Goyim was NOT for the sake of the Goyim, but for our OWN sake, that we dont end Golus early. It says this in every single interpretation in the commentaries about the Oath. It was not for the sake of the Goyim but for us. So just because the Goyim violated their Oath and hurt us does nto mean we can violate another one and hurt ourselves more! Shevet Efraim left Egypt in violation of the Oaths. Egypt surely violated their Oath when they tortured Jews for centuries. Yet Ephrain, Chazal say, were all hunted donw and killed in the deset for violating their Oath by leaving Egypt early. The Oaths are brought down l’halachah in Rishonim and Achronim as viable and very real. This, despite the fact that the Goyim have been violating their Oath for thousands of years. And besides all this, the second Oath, nshelo yaalu b’chomah has nothing to do with the Goyim, and woud not be dependent on the Goyim’s Oath.
The Maharal and R. Yonason Eyebushitz write that even if the Goyim give us permission to take Eretz Yisroel we are not allowed to do it. Better we should die than take Eretz Yisroel, the Maharal says. And the Gemora itself disproves the idea, since the Gemora says that the reason Chazal commanded us not to go from Bavel to Eretz Yisroel is due to the Oaths, even though Bavel violated their Oath for sure with the atrocities they committed during the Churban (The Shulchan Aruch writes that the Brachah of Vlamalshinim was enacted to praise Hashem for destroying the evil kingdom of Bavel). The Gemora then asks on R. Zaira who says that the Oaths only include not taking Eretz Yisroel forcefully, but the Oath not to rebel against the nations is not included. The Gemora could easily have answered that Bavel violated their Oath and therefore our Oath of rebelling against them is null. But the Gemora says no such thing. R. Avrohom Galanti (Zechus Avos) brings a story of the people of Portugal who wanted to defend themselves against the government by making a rebellion. The government then was making forced SHmad and all sorts of persecutions. They asked the “shem hameforash” and were told not to do it because it would violate the Oaths.