I'd say that a happy ending is possible, I mean, even in noir stories happy endings are not unheard of, but is usually behind extreme struggle, struggle you just barely survive, let alone you are your lover together, but it's possible, just depends on how you played your cards
And yeah, I absolutely love noir novels, they're so intriguing, thrilling, not knowing who you can trust, if anyone at all, friends turning up to be foes, foes turning up to be allies and that sort of thing, you can never be sure of anything and at times you can't even trust yourself, the makings of a perfect noir, added with clever plot twists and cliffhangers
But I too am a sucker for happy endings, otherwise the struggle was in vain, right?