The attack on Fort Sumter insured the survival of the CSA. Without the attack, the CSA would have remained a handful of bickering States whose survival would have been dubious. The attack brought in VA and the other Upper South States; it allowed a state of war which allowed dissent to be suppressed; nothing like a war unites a country and it gave a legitimacy to the Davis administration who had been appointed president and and no popular mandate. Without the attack, Davis would have been viewed as a weak president. The attack also improved the chances for foreign recognition.
Too many benefits to attack, too many liabilities if no attack. Unless Lincoln surrendered, the attack was going to happen.