Did you try getting the Leadership Magazine at Silver Strip (Or was it Platinum strip) in a Bingo place just opposite a bar? It helps a lot to bring Survivor around with you. If I'm not mistaken there are about 10 survivors that do not appear in missions but rather you have to look out for them around the entire area at different times.
And, it is very possible to save everyone without the need to sacrifice (Well, there are three survivors that are particularly annoying to get them as you have to gamble with them at Poker and actually have to beat them to it! You need the three gambling magazines to make it easier.)
Theres Tape it or Die crew on the third(or fourth i forget) day they dont pop up on the quest log and you can save them on the final day theres Snowflake and Lenny that never pop up and finally theres the High Rollers poker club that never pops up that you have to say :) google em
Now you Know!~
(theres also soldiers that need rescued on the final day before the Overtime mode and on the WWJWD? theres a man hiding)