The command to promote leader is

/pr

I don't know how you'd get it to pick between dead or alive. Maybe with


/clearfocus
/focus [target=main, exists, nodead][target=slave1, exists,
nodead][target=slave2, exists, nodead][target=slave3, exists, nodead]
/pr focus

or

/target [target=main, exists, nodead][target=slave1, exists,
nodead][target=slave2, exists, nodead][target=slave3, exists, nodead]
/pr target


or something like that.