Apne awatar ka uddeshy samapt hone par unhone Nar aur Pashu ka rup tyag apne vastveek swaroop ke darshan Prahlad ko dekar anterdhyan ho gaye.
Ek bat spast kar lo Pravin, Avtarwad ka tatpary hi hai ki ' NEESHCHEET KARAN SHE DHAR STHAPNA KARNE EVAM ADHARM KA NASH KARNE PRABHU AWATAREET HUYE, ya prakat huye....Sirf Krishnawatar main hi unke vaikunthgaman ( Mratyu ) ka varnan hai , ishi karan Krishn Awatar ko PURN-PURSHOTTAM AWATAR kaha jata hai.
Your vote on this answer has already been received
One must understand that the main aim of the almighty in any avataar is SISHTA RAKSHANA i.e protection of the pious. narasimha avatar in this context came to protect prahlada and for that end killed hiranyakasipu. thus dushta sikshana or punishing the wicked becomes an ancilliary aim. since this particular avatar did not take an ordinary birth nothing can be said about its parisamaapti. after the slaying of hiranyakasipu the lord took his original form ( as per bhagawatam) of vishnu, blessed prahlada made him the emporer of the 3 worlds and went back to his dhaam. but this avataar has got certain qualities whcih make him very popular among his devotees. a bhaktha vatsala - loves his bhaktas extremely. his power is sometimes superimposed on his bhaktas who demonstrated super human strength ( pl. read how sri adi sankara was saved from the followers of chandi sampradaya by one of his sishyas- i think it was padmapada.) . so this is one lord ever present and manifest in that form to his