Gazprom is not a stable energy partner. I believe that they have proved this over and over again in the past six months. They have used their control of energy as both political and diplomatic leverage (e.g. Ukraine, Byelorus, etc.).
But, as "Valery Nesterov, oil and gas analyst at Troika Dialog" says,
Given that Iran has the world's second largest gas reserves after Russia, "what alternatives does Europe have?"