There is a difference if he promised something and does not fulfill it.
Yes, but He didn't promise everything. He only promised the Qaim comes. But what Qaim does, who He is, or what happens after Him, is not a promise. It was upto Him how He wanted to be. He possesses Bada, exactly for this reason.
It is narrated from Ibne Walid from Saffar from Ahmad bin Husain from Uthman bin Isa from Khalid bin Najih from Zurarah bin Ayyan that he said: Imam Ja’far Sadiq (a.s.) said:
“There is an occultation for the Qaim before his reappearance.” I asked:
“Why is it so?” He replied: “He is fearful.” And he pointed towards his belly,
implying that the Qaim fears for his life. Then he said: “O Zurarah; and he is
that awaited one and he is the one in whose birth they shall doubt. Thus some
will say: His father died heirless and some will say: He was in the womb of
his mother when his father died. Some others will allege that he was born two
years before the passing away of his father. And he is the Awaited one;
but
the Almighty Allah likes to test the Shia. It is the time when people of falsehood will fall in doubts.”
It is recorded in Bihar alanwar, vol 52-3:
Have you not considered those who went forth from their homes, for fear of death, and they were thousands, then Allah said to them, Die; again He gave them life…” (Surah Baqarah 2:243)
These were the verses in support of Rajat. Now the Messenger of Allah (s.a.w.s.) says:
On Judgment Day the arrogant will be raised in the form of a tiny ant.
Also the Holy Prophet (s.a.w.s.) said that
all that happened in Bani Israel,
will also happen in my Ummah; like the splitting of the earth, transmogrification of the people and the dropping of stones etc.
Huzaifah says that
it is not unlikely that the Almighty Allah should raise
most people of this Ummah in the form of monkeys and pigs. So the Rajat
that I believe, is also proved from Quran and traditions of the Prophet and I
am certain that the Almighty Allah will send Sawwar to the earth in form of
dog, pig and ant, because he is unjust, arrogant and infidel.
Through his chains of narrators, it is narrated from Abu Khalid Qummat from Humran bin Ayyan that:
“Once I asked Imam Muhammad Baqir (a.s.) if there is something in Bani Israel, which will not happen in this Ummah?
He replied: No.
I asked: Then what do you say about the following words of the Almighty Allah?
أَلَمْ تَرَ إِلَى الَّذِينَ خَرَجُواْ مِن دِيَارِهِمْ وَهُمْ أُلُوفٌ حَذَرَ الْمَوْتِ فَقَالَ لَهُمُ اللّهُ مُوتُواْ ثُمَّ
أَحْيَاهُم
Have you not considered those who went forth from their homes, for fear of death, and they were thousands, then Allah said to them: Die; again He gave them life…” (Surah Baqarah 2:243)
Did they die on that day or they had returned to the world?
No, they had returned to the world, lived in their houses, lived a normal life as long as Allah willed and then died when their death arrived.”