If you want to have a baby by a sick or dying man, can sperm be taken to be used later?

I’ve always wanted to know what would happen if the man I want to have kids with got sick or shot or something. Is there anyway I could still have his kid? I think about this especially when people die and their girlfriends/wifes/fiances are not pregnant and they have no other kids. I want to have kids by my boyfriend and we plan to do that whenever we get married but if something were to happen to him before we get married, I wonder if I could still make that happen??? Just curious.