Can a patient with congenital neutropenia survive long without a spleen if it has to be removed due to extreme enlargement?

Usually yes. But each case is different, and the answer might depend a lot on the reason for your the enlarged spleen. This is something to discuss with your doctors, ideally both an infectious diseases specialist and a hematologist/oncologist; and perhaps a gastroenterologist, e.g. if he splenic enlargement is related to liver disease. Good luck.