1. If they were replaced by other players then no. Like in baseball, in soccer once you're substituted by another player you can't be put back in the game. It is possible that players are temporarily injured and they go to be treated momentarily at the sidelines, leaving the team shorthanded for the duration, then once they're fine again the ref will signal for them to join the action again.
2. Offside, Ziyech I think it was, he was ahead of the defensive line when the ball was kicked in his direction so even though he scored a banger he was in an illegal position to begin the play. Thus the goal never counted.