The majority of scholars from the Maliki, Shafi'i, and Hanbali schools hold that ritual purity (tahara) is a condition (shart) for the validity of Tavaf, meaning Tavaf performed without abdest is invalid and must be repeated. Their primary evidence is Hz. Peygamber's statement that Tavaf is like namaz, and since namaz requires abdest, so does Tavaf. Additionally, Hz. Peygamber (sallallahu aleyhi ve sellem) himself performed abdest before his Tavaf and instructed Aisha to do the same.
The Hanafi school takes a different position: they consider abdest for Tavaf to be farz (wajib) but not a condition for validity. This means that if someone performs Tavaf without abdest, the Tavaf is technically valid but the person has committed a sin and must offer a penalty sacrifice (dam). This distinction can be relevant for hacilar who find themselves in difficult situations regarding maintaining abdest in massive crowds.
If your abdest breaks during Tavaf, according to the majority position, you should leave the Mataf, perform abdest at the nearest facility, and then resume your Tavaf from the circuit where your abdest broke — you do not need to restart from the beginning. Wudu facilities are available throughout the Haram complex. Given the extreme heat and physical exertion, carrying a small water bottle and making abdest before starting Tavaf is essential planning.