How to make so when all players except for one die, everyone gets teleported by command block

You can set up a counter for players with at least 1 life left using /execute. I'm using your existing lives objective here.

In 1.8, this is arguably best done using an armor stand to hold the score:

/summon ArmorStand ~ ~ ~ {CustomName:"playersLeft",Marker:1b,Invisible:1b}

Now, create a clock and run:

/scoreboard players set @e[type=ArmorStand,name=playersLeft] lives 0 
/execute @a[score_lives_min=1] ~ ~ ~ scoreboard players add @e[type=ArmorStand,name=playersLeft] lives 1 
/execute @e[type=ArmorStand,name=playersLeft,score_lives=1] ~ ~ ~ <your command>

What happens is that the armor stand's score is set to 0, and then incremented by 1 for every player that has at least 1 life left. Your command is then run when the armor stand's score is (at most) 1.

In 1.9, you can use the magic of conditional command blocks to skip the armor stand and use a fake player instead. Set up a repeat/chain line and run:

/scoreboard players set #playersLeft lives 0 
/execute @a[score_lives_min=1] ~ ~ ~ scoreboard players add #playersLeft lives 1 
/scoreboard players test #playersLeft lives 1 1

Then, place your command in a conditional chain command block at the end of this line.