I think there's a niche for everyone. You just have to be true to your audience if that's what you're doing. Romance, as a genre, practically requires a happy ending. Happy for now or happy ever after.

But not all genres work that way. Check out the competition for any niche and don't make me bring up random titles that won't fit the rating. If they're making readers happy - you will, too.

I'd be more upset to have an author be doing the HFN until they "made it" then switched to tragedies. If I preferred tragedies, I won't be reading you because you stuck To happyr ends.