Mishnah Berurah — משנה ברורה

Even though most of it fell off - The Ta"z and Eliyah Rabba argue on this (against the Mechaber), and also the Gr"a leans towards the opinion of the Ta"z. But according to everyone, if it fell off one's entire body... even though it remained in his hand, he needs to make a blessing on it... for the מצוה has left; Since the main מצוה of wrapping is [around] one's body. If one made the blessing on the טלית, and it fell out of their hand before they wrapped in it and [then] they picked it up and wore it, there is no need to make the blessing again. And [this is] even if the ציצית became invalid right then, and he had [other] ציצית [strings] available and fixed them immediately... [in such a case] he does not need to make the blessing again; since he did not yet do his מצוה, he did not take his mind off of it [just like by תפילין [as seen] later in Siman 25 Se'if 12, see there in the Ta"z - Sei'f Kattan 12]. And someone who took a טלית to wrap in it and starting making the blessing... and before he could finish the blessing, it (the טלית) was taken from him... and his תפילין were in front of him... he may complete the blessing as "אשר קדשנו במצוותיו וציוונו להניח תפילין ("Who has sanctified us with His commandments and commanded us to don תפילין")... and he fulfills his obligation with that [Hilchot Ketanot Siman 153, and the Ohr Hachaim agreed with him as to what the actual law is.