Assad's negotiation team will demand as a precondition for any agreement that Assad remains in power, and no elections to replace him. They will be supported in his demands by Russia, Iran, and China.
The rebel negotiation team will demand as a precondition for any agreement that Assad steps down immediately and elections held to choose a successor. They will be supported by the Sunni states, most of Europe, and the USA.
The radical Islamists will declare the negotiations null and void because they weren't included, even if they would come, which they won’t. They will demand the immediate conversion of Syria into an Islamic caliphate.
The diplomats and politicians will announce that the talks are successful, having succeeded in agreement on most issues with only a few remaining to be resolved in further negotiations.