What you are saying then, and correct me if I am wrong is that you do this...
5 man unit with libby, takes 10 wounds, ap3.
1: roll 2+ 10 dice, fail 5
2: libby is in front, so his armor save is rerolled. You reroll 5, still fail 3.
3: you can then LOS (correct?) On another 2+, he fails 2, so takes a wound
4: 2 other termies now die.
What that effectively does, is give the entire squad a 2+ re roll....that cannot be right. The way magpie described makes the most sense. Roll all die, los and those that fail go on to kill a terminator, then reroll the failed armor on the libby.
I am not talking about what is written in the rulebook what I am talking about is an expedient method of rolling the dice.
1. Rolling all the armour saves is fine as they all have the same armour save, no worries there.
2. The Libby is in front so what he now needs to do is take each failed armour save in turn and decide a) LoS or b) re-roll armour save. If he takes the re-roll before the LoS he is effectively giving the guy he passes the wound to a re-roll, albeit one that he fails.
i.e. there is an extra die roll in there (the re-roll) that shouldn't be there which will alter the probabilities of the resolution.
If it is the other way around tho' you could
1. Roll all armour saves, any that fail go to:
2. The closest character who doesn't have a re-roll, LoS the first wound onto the Libby, who can then take the re-roll.
repeat step 2 for each unsaved wound.
This is no different to : first wound to closest mini, roll LoS, roll Armour save on libby, re-roll armour save on Libby. You are rolling 3 dice, in the previous example you were rolling 3 dice when you only want to roll 2.
You can't take all LoS in one hit because if you fail the first two the front mini would already be dead (on a 2W mini) so the remaining wounds would be placed direct on the next mini. If you fail the last 2 then there are no more wounds to deal with.