What are the ramifications of "Vetiharo"?
Seforno: The Kohen purifies him from P'ri'ah and P'rimah. 1
Permitting him to wear clothes that are not torn and to cut his hair.
What happens to the dead bird and the live bird?
Targum Yonasan: The Kohen buries the dead bird in the presence of the 'Metzora'. 1 If the live bird returns, it may be eaten.
Kidushin 57a-b: "Kol Tzipor Tehorah Tochelu" includes the live bird. "V'Zeh Asher Lo Sochlu" (Devarim 14:11, 14:12) includes the dead bird. We do not say oppositely, for the Torah would not command to send the live bird for a pitfall 2 (one who finds it would assume that he may eat it).
Why does he slaughter one bird and send away the other?
Targum Yonasan: In the event that the Metzora does not do Teshuvah and the Tzara'as is destined to return, the bird will return to him in his house on that day. 1
Moshav Zekenim: He sends it to the field, to hint that he should engage in Torah, which is Hefker like a field.
Moshav Zekenim (4): Hashem gives to [the Metzora] a sign - just like the bird slaughtered and buried in the ground cannot move from its place, so Tzara'as cannot come on him again (if he will repent - Da'as Zekenim 5), If you will say that [no matter what] it cannot come again, look at the bird that was sent. If you retract from your Teshuvah (and speak Leshon ha'Ra again), Tzara'as will return to you.
Moshav Zekenim (4, citing R. Eliezer of Garmaiza): The birds hint to the Yetzer Tov and Yetzer ha'Ra. The Torah teaches how to rule over them. He slaughters one (the Yetzer ha'Ra) over a Kli Cheres. Man is compared to a Kli Cheres; once it is broken, it cannot be fixed. Through this he kills and lowers the Yetzer ha'Ra. He slaughters it over Mayim Chayim, i.e. Torah; if this disgusting one (Yetzer ha'Ra) encounters you, drag him to the Beis Midrash.
Kli Yakar (4, DH v'Ta'am), Me'am Lo'ez (21): There are two kinds of speech. One is forbidden, e.g. Leshon ha'Ra. This must be slaughtered (eradicated). The other is a Mitzvah - Torah and Tefilah. This must be joined to cedar, crimson thread and hyssop, i.e. humility 2 ; even in Torah, one's heart must be broken. We sprinkle on him using the live bird and the blood of the dead bird, for he must repent for his past and fix his future.
May the live bird be eaten?
Targum Yonasan: Should the bird return it may be eaten. 1
See Peirush Yonasan and Torah Temimah.
Why does he sprinkle on him seven times?
Moshav Zekenim: [This hints that] he should engage in the seven Chumashim, according to the opinion that Parshas"va'Yhi bi'Nso'a ha'Aron