The collapse of the Assad regime was never going to be swift. Since the early days of the uprising last March, my feeling all along was that it wouldn't happen this year. And even if it were to happen tomorrow, the opposition is sill far from ready to take over. 

Next year, though, is a different matter. Twelve months from now, it's hard to imagine that Assad will still be clinging on. Barring a Libya-style military intervention, which at present seems very unlikely as well as unwise, there are three main factors that will determine how long it takes.

The first is the strength – or weakness – of the regime's support base. Broadly, these are the Alawites who represent 12%-15% of Syria's population. But in an article for Foreign Policy, Bruce Bueno de Mesquita and Alastair Smith (authors of The Dictator's Handbook) argue that Assad's "key backers" number no more than 3,600. These are the people whose loyalty is essential to keep him in power, and who will stay loyal only so long as he looks after their interests:

"If he betrays the interests of his closest Alawite allies, for instance by implementing reforms that will dilute their share of the spoils, they will probably murder him before any protesters can topple his regime ... Should the loyalty of his 3,600 supporters falter and they stop working to neutralise protest, Assad will be gone immediately."

This means that reforms, on a scale that would satisfy the protesters (including renouncing the supremacy of the Baath party), are not a practical option for Assad. At the same time, he has to continue delivering economically for his support base – which is proving increasingly difficult.

The second factor, noted by Joshua Landis on the Syria Comment blog, is "the steady erosion of state authority and national institutions, as the opposition, which remains largely organised on a local basis undermines central authority at many points". 

Landis continues:

"Neighbourhood committees and armed groups are forming in ever greater number. Most use the word 'coordinating' in their title, but few relinquish local authority. They prefer to keep decision-making local and in their own hands. 

"Some of this is for practical reasons. Spies are everywhere. I am told by good sources that one of the leading reasons why Aleppo has been so quite is that the local coordinating committees recently discovered that their efforts to put together surprise demonstrations were being foiled by informants. One recent opposition statement admitted that their ranks have been riddled with informers."

The third – and perhaps most crucial – factor is the decline of Syria's economy which simultaneously threatens to weaken Assad's support base while spurring on the opposition.

Landis writes:

"The international community has isolated Syria and continues to tighten sanctions and force western companies to withdraw from the country, which is causing the economy to contract rapidly. Syria’s GDP has shrunk by almost 30% in dollar terms since the start of the year – from $55 billion to $37 billion dollars, as the Syrian pound has collapsed from 47 to 62 to a dollar. Heating oil has all but disappeared from the market place; people are cold. Cooking oil is scarce and electricity in many cities is cut for hours on end during peak usage periods."

To counter the effect of sanctions, the regime is getting some external support. Bueno de Mesquita and Smith point out that in July Iran offered $5bn in aid, with $1.5bn paid immediately: 

"The $5 billion is equal to about 40 percent of Syrian government revenue. Since the announcement of Arab League sanctions, Iran, Iraq, and Venezuela have signed agreements to expand trade and investment in Syria to the tune of more than $7bn in 2012, including building an oil refinery. 

"That is just what Assad's political-survival doctor ordered. This injection of cash in the short term is likely to keep the military and security forces on his side. The military core of his coalition is likely to do whatever it takes to keep the president in power as long as that money keeps on flowing."

So one question is how long this external support will continue. The Venezuelan president, Hugo Chavez, has been seriously ill and if he were to die that source could easily dry up. Iranian support cannot be taken for granted either. With or without Assad, Iran has to coexist with its Syrian neighbours. Once the Tehran regime decides that Assad is definitely on the way out, it will probably abandon him and start building bridges with his likely successors.

NOTE: Because of a typing mistake, this article initially said that Iraq had offered $5bn aid to Syria. The country offering it was Iran, and this has now been corrected.