There is a story of Agastya muni. He saw his ancestors lying upside down without attaining salvation. They said that it is because there is no one to continue their family because Agastya muni did not have siblings and he himself was unmarried and celibate. Adi Sankaracharya did not have children despite being an only son.Chaitanya mahaprabhu was the 10th son but his parents did not have grandchildren(since 8 sisters died and elder brother took sannyas). Is it a "sin" if there is no one to continue the family?
No, certainly not.
According to our culture,
putraarthe kriyate bharya (Manusmriti), meaning marriage is for begetting a son.
The importance of son is
putra(son) uplifts from the hell named put : Reference : http://sanskritdictionary.com/?iencoding=iast&q=पुत्र&lang=sans&action=Search
On the otherhand, the glory of brahmacharya is sung as
na tapah tapam iti aahur brahmacharyas tapottamamm/urdharetaa bhabed yastu sa debah sa na manushah// meaning : no austerity is as great as brahmacharya.The Urdharetaa is god, he is not a man.(Reference : Omkarnath Rachanavali, volume 6, page 347.
yad idam brahmano valam brahmacharyam iti smritam/param tat dharmasarvebhyo tena yanti paraam gatim//(Mahabharat), meaning : The power if Brahman is inherent in brahmacharya. There is no spiritual practice greater than this and brahmacharya liberates one. (Ibid. page 347).
So a real brahmachari is a living god, a jivan-mukta. He has no need to get uplifted from hell, he can uplift many from hell.
And 'Naisthika brahmacharya' is no less in glory than sannyasa. Many saints like Sri Balananda Brahmachari, Sri Mohonananda Brahmachari, Sri Prabhudutta Brahmachari etc were naisthika brahmacharins throughout the entire life : they had no need of taking sannyasa.