Must one complete the prayer when ablution is nullified, or must it be resumed anew? And when does the follower say the taslim in a loud prayer?

Whoever nullifies their ablution due to flatulence or anything else during prayer should leave, perform ablution, and then return to resume the prayer from the beginning, according to the preponderant opinion of scholars. This is the madhhab of the Malikis, Shafi'is, and Hanbalis. Their argument for this is that an impurity (hadath) invalidates both purity and prayer, by analogy with intentionally performing an act of impurity, which invalidates prayer by consensus. The majority of scholars cite the hadith of Ali ibn Talq (may Allah be pleased with him), who said that the Messenger of Allah (peace and blessings be upon him) said: "If one of you passes gas during prayer, he should leave, perform ablution, and repeat the prayer." As for the Hanafis, they said one could continue building upon the prayer, citing the hadith of Aisha (may Allah be pleased with her): "Whoever is afflicted by vomiting, nosebleed, regurgitation, or madhy (pre-seminal fluid) should leave, perform ablution, then build upon his prayer, and he should not speak during that time." However, this hadith is weak. As for the congregant (ma'mum), it is preferable for him not to make the salutation of peace until the Imam finishes the second salutation.