Actualle, asisecanta, there are two endings - the one I usually sing is more Traviata-esque. Magda realises that she will never be acceptable as Ruggiero's wife because of her past, and she leaves him to continue her journey "come la rondine" moving with the seasons.
Not sad at all - it's a passionate, slightly obsessive, very young girl, used to getting her own way, and desperate to see the charismatic, warm man she has a serious crush on!
I think the person who thought this is sometimes sung by a mezzo is mixing up the title role in this opera - Herodiade - and the role of Salome from which this aria comes. Larger soprano voices often have a darker 'colour' which can make them sound mezzo-like. As for the various comments regard...
Please note that the extraneous sound you may hear is that of my jaw dropping. Wow! And this is Handel?!?!?!?