You know that happy, bittersweet feeling you get after finishing a particularly delicious story arc, where you empathize so strongly with the characters you can't help but hope their lives are forever fulfilling and wonderful? Well that's a metaphorgotten but this elicited the same feeling of warmth and completion that finishing Fate/Stay Night, Harry Potter, or any other story fully fleshed out from beginning to epilogue did.
In other words, contentment until you want to delve back into the world of their story, at which point it turns into a sad melancholy when you're only able to re-experience the same events that led you to love them instead of following the characters onto a new journey.
So yeah sequels would be nice.
But unnecessary; this story is finished.
And very good.