Once searched do the search cards remain available to the player until they are used?
Or are they returned to the deck after the XP/Gold is rewarded after the quest?
They are returned to the deck at the beginning of Campaign phase after quest even when unused.
Also if the number/reward in the lower corner says 25, is that more gold per player or just 25 total when it is awarded?
Heroes as a team recieve gold equal to the amount printed on seach cards they got. For example, if 25 printed on search card, heroes will get 25 gold, not 25 per hero.
Core Rule book, page 20.
The Campaign Phase
After each quest of a campaign, there is a Campaign phase...
1. Receive Gold from Search Cards: Record the total gold value of every Search card the heroes acquired over the course of this quest on the Campaign sheet (even if the Search card was used during the quest). Then return all Search cards to the deck (even if the heroes didn’t use their abilities). The heroes are assumed to sell their newly discovered treasures in Arhynn.