does existing zone hero get sacrificed? or can new hero not enter?
playing a hero to zone with hero
New hero can not enter.
FAQ p.8
Limit 1 Hero per zone
If a player has a copy of a Hero in
play, he cannot play, take control of,
move, or put into play (via a card
effect) another Hero into that zone.
His opponent also cannot play, give
control of, move, or put into play (via
a card effect) another Hero into that
zone.