How can one reconcile two narratives, one of which states that the Companions were around Aisha when she lost her necklace and the verse of tayammum was revealed, while the other mentions that they left her and departed during the incident of the Ifk?

The preponderant view is that the story of Aisha losing her necklace during the incident of the Ifk (Slander) (Battle of Banu Mustaliq/Al-Muraysi' in the fifth year of Hijra) is different from the story of her losing her necklace that led to the revelation of the Tayammum verse. The latter occurred in a later battle, most likely the Battle of Dhat al-Riqa' (in the seventh year of Hijra). This distinction is supported by Abu Bakr's statement to Aisha, "Is there trouble and tribulation for the Muslims because of you on every journey?" and by Usayd ibn Hudayr's statement, "This is not the first of your blessings, O family of Abu Bakr."