If one davens a long SE on YOM KIPPUR and misses the prayers (Selichos) that are said during chazora, does he need to make them up later?
May one daven Neilah at great length and miss Maariv with the minyan, or should one avoid doing so?
If you miss some of the selichos during the davening, you can daven with the tzibbur, and you don’t have to make it up later, because you will miss out on other tefilos.
If someone is davening neilah and he started with the tzibbur and the tzibbur is already up to maariv, he may continue davening, no different than the fact that he is missing kedusha and kaddish of neilah. He is only obligated to abstain from starting to daven if he is starting to daven later than everyone else.
Biur Halahcha 109 D:H Hanichnas, Aruch Hashulchan 109-5, Simlas Chaim 126, Orchos Rabeinu 3-pg. 208.