A2 That depends on GM adjudication. I've seen it played both ways, actually where the spell remains until it is successfully employed or until the cleric casts a different spell and that if you miss on the attack roll, the spell is wasted. Something to ask the DM about.
Personally, I've ruled it both ways myself, depending on the tone of the campaign. Dark and gritty type of campaign generally means that it'll be wasted. More superhero style? Might be a bit more persistent.