If a man says “this is my todah – my thanksgiving offering – and these are its accompanying loaves,” if the loaves are misplaced, he must replace them, but if the sacrifice is misplaced he does not bring another animal instead.
He explains the reason for this: The loaves come as an accompaniment for the thanksgiving sacrifice; the sacrifice does not come as a consequence of the loaves.
The aharonim point out that when Rabbi Aba rules that the owner of the sacrifice does not replace the lost animal because of the loaves, that only means that he is not required to do so. As Rashi explains, the fact that the loaves are still extant does not require a korban todah to be brought, but the owner can choose to replace it if he wants. Nevertheless, according to the parallel discussion in Masechet Pesachim (daf 13a) in the event that the sacrifice is lost, the loaves cannot be used for a different korban todah, since these loaves were intrinsically tied to the missing sacrifice, so they will have to be redeemed for money, at which point they lose their sanctity and can be eaten in an ordinary fashion.
The Sefat Emet explains that the fate of these loaves may depend on the language that was used at the time that they were sanctified. If the owner of the sacrifice said “these are the loaves that are to accompany the korban todah” then they are tied to the sacrifice and cannot be offered with another. If, however, he said “I accept upon myself to bring loaves to accompany the korban todah” and afterwards he sets those loaves aside for that purpose, since he accepted the obligation on himself the loaves remain an independent obligation and they could be attached to a replacement korban todah.