Option 1 -> "am to leave" is present tense and doesn't match the past context of the sentence.
Option 2 -> "was to have left" correctly expresses a past plan or intention that was not fulfilled.
Option 3 -> "would leave" suggests a conditional or habitual action but doesn't clearly indicate an unfulfilled plan.
Option 4 -> "will be leaving" is future tense and contradicts the past events described.
Hence, Option 2: was to have left -> The structure "was to have + past participle" is used to express a past arrangement or plan that did not actually happen. The speaker had planned to leave on Thursday, but due to having a cold, the plan was not executed and was postponed to Saturday -> correct