Or it could go down one of two ways..
Nick has the Holy Grail now, what he said he wanted, but not whathe wanted. If Michael is right, that object if it is a weapon, isn't a conventional one. It might backfire and Nick will give that coin up, plus his own.. He might even wield the Sword of Love in the end, because in spite of everything he did still love his daughter. Yeah, I know, unlikely, but had to put it down...
Or more likely;
Nick is isolated, he has been brought down and is at rock bottom.. He wants revenge...He knows now about the love between Harry and Murphy. He lost his love, he knows tricking Harry into picking up a coin doesn't work.. So for the sheer revenge factor, he finds a way to trick Murphy into it.. She's been hurt, she made a couple of poor decisions regarding the Swords, she may never be as effective [because of injuries] physically as she once was.
All of the above, even if her and Harry get together, make her vulnerable to Nick possibly tricking her into picking up the coin. Revenge not just on Harry, but on her as well.