I say, and with Allah's success: No, it is not an excuse, for the person in i'tikaf does not visit the sick, and even if some time is spent in leaving his i'tikaf, even if he was forgetful, it invalidates his obligatory i'tikaf which is vowed, and he must make it up; as narrated by Aisha, may Allah be pleased with her, who said: “The Prophet (peace be upon him) would pass by the sick while he was in i'tikaf, and he would pass by as he was, without stopping to ask about him.” This is found in Sunan Abu Dawood 2: 333, and Sunan al-Bayhaqi al-Kabir 4: 321. As for the confirmed Sunnah i'tikaf and the recommended one, it ends with his exit without an excuse. Refer to: Al-Mabsut 3: 118, and Al-Tahbih 1: 351, and Allah knows best.