Is a happy ending obligatory in novel writing? Of course not. Novel plots can end any way you like. But before you dismiss writing a happy ending for your novel out of hand, consider your options...
One extreme is what might be called a Hollywood-happy ending. You know the kind I mean - these endings aren't just happy, they leave you with tears spoiling your shirt and a lump in your throat it takes until morning to shift.
At the other end of the scale of endings in novel plots is the one that is so bleak it is empty of all hope. This variety might leave you in tears, too, but more likely you'll just feel miserable.
Now, there is nothing wrong with either of these endings. Your genre or subject matter or sensibilities as an artist might demand that you choose one or the other.
But if you want me to make a recommendation, I would suggest you avoid either of these extremes in your novel writing career...
The best kind of novel plots, in my opinion, are natural and credible ones, not artificial ones. Ending them in one of the two ways suggested above - happiness tempered by loss or sadness with hope on the horizon - will ensure that they are natural.
"I dislike the conventional 'happy ending' with all the pink bows neatly tied, but I think the reader should feel there is the hope of something better in the future and that the main character has gained something of value from his experiences."
- Dianne Doubtfire
Next Step: Now it is time to consider a different kind of ending altogether - "Deus Ex Machina" Endings...