AFAIK, you need to rescue at least 3 hostages in order for it to count as a win. Unless there was a change to the config that allows only 1 to be saved.

I remember back in the old days in 1.5-6 on cs_militia, it was almost impossible to rescue all of the hostages, and sometimes we'd just wallspam the garage to kill that last one. Ahhhh... memories.

EDIT: Hostie maps are shitty as fuck, anyway.