Brahimi, who is in Syria on the most sensitive leg of a regional push for peace talks, has been seeking to build on the momentum of last month's US-Russian deal to eradicate Syria's chemical weapons in order to launch the so-called Geneva II peace talks proposed for next month.
But the talks have been cast into doubt by the increasingly divided opposition's refusal to attend unless President Bashar al-Assad agrees to step down, a demand rejected by Damascus.
In an interview with a French website published Monday, Brahimi said Assad could contribute to the transition to a "new" Syria but not as the country's leader.
"What history teaches us is that after a crisis like this there is no going back," the Algerian diplomat told the Jeune Afrique website ahead of his first visit to Syria since December, when he angered the Syrian government by insisting that all powers be handed over to a transitional government.
The veteran troubleshooter admitted "the entire world will not be present" at the talks, but said the alternative to a political settlement could be a failed state in the heart of the Middle East.
"The real danger is a sort of ‘Somalization,’ but even more deep and lasting than what we have seen in Somalia."
More than 115,000 people are estimated to have been killed in Syria's 31-month conflict.
In the latest blow to peace efforts, 19 extremist militant groups issued a statement Sunday saying anyone who attends the Geneva talks would be committing "treason" and "would have to answer for it before our courts," implying they could face execution.
Russia denounced the warnings, saying it was "outrageous that some of these extremist, terrorist organizations fighting government forces in Syria are starting to make threats."
"So you can say that Geneva II is almost totally rejected within rebel ranks," said Thomas Pierret, an expert at Scotland's Edinburgh University.
"If some of the opposition does take part and reaches an accord, it will be worthless."
Under pressure from its Western backers to attend, the so-called Syrian National Coalition, an umbrella opposition group, is to meet on November 9 to decide whether to take part.
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