I’m not sure how being diagnosed early means they will survive? Not with a 50 to 90% mortality rate.
They will have a better than 50% chance, and there chances will be increased simply by having the right IV and oral hydration and minerals. Virus inhibitors will help. But mostly it is up to each individual and how their immune system reacts. The virus attacks the imnune system in various ways so immune system strength is not the key factor, but rather the particular way the immune system reacts.