Once Relic Golem has attacked, causing its first ability to apply by removing cards from graveyards won’t cause Relic Golem to be removed from combat.

Similarly, once Relic Golem has blocked an attacking creature, causing its first ability to apply won’t cause that attacking creature to become unblocked or remove Relic Golem from combat.

An ability that offers a bonus if an opponent has eight or more cards in their graveyard won’t provide additional benefits if more than one opponent has eight or more cards in their graveyard. There are also no additional benefits no matter how many cards are in an opponent’s graveyard, as long as there are at least eight.

In a multiplayer game, once an opponent leaves the game, they won’t be considered for such an effect, no matter how many cards they had in their graveyard before leaving the game.