Slightly edited to improve readability
No, they cannot.
If a meditator becomes a Sotāpanna, a stream-enterer without fruition, what will happen is that at the point of the dissolution of the body, at the point of death, they will attain fruition of Sotāpanna at that point in time.
Their attainment, once they become a stream-enterer, is basically set. It’s not like they can go back, and the lower realms will no longer be open for them.
At the dissolution of the body, they will attain fruition of stream-entry, which is where it becomes solidified. The doubt goes away completely, there’s no more identity view – where there’s a sense of permanent self in anything – and of course the belief in rites and rituals are completely eradicated. Even in the entry into the Path, those fetters are destroyed. The fruition is basically what just solidifies it.
But I also want to give one little caveat here that the Path and the Fruitions are not always so clearly defined in the suttas. There is mention of the other levels of sakadāgāmī and anāgāmi, and there might be some places where they do talk about Path and Fruition, but they’re not so clearly defined.
Having said that, as I said, once you become a stream-enterer and you pass away without attaining anything further, at the level of death, at the point of dissolution, you will still have the fruition. And you won’t have any more that potential of entering any of the lower realms, below the human realms.
Fruition is experiencing Nibbāna the second time.
Can one experience Nibbāna without attaining the next stage?
No, once you have a Nibbāna experience, that unlocks, so to speak, the next attainment for you.
And then, at the level of arahantship, you can continue to attain Nibbāna over and over and over, make it your object of meditation, conventionally speaking. But that’s the end of the Path, that’s the Fruition of the Path.
So, every time you attain Nibbāna, it’s the unlocking of a new attainment, until you have full fruition at arahantship.