Both these words, ikiwakare and seibetsu, refer to people becoming separated while still alive, but the JapanDict definition of both is "lifelong separation". This seems to be incorrect, looking at the weblio.jp definitions:
https://www.weblio.jp/content/%E7%94%9F%E3%81%8D%E5%88%A5%E3%82%8C
https://www.weblio.jp/content/%E7%94%9F%E5%88%A5
