There seems to be at least one positive to death: the end of the struggle. If you don't exist you don't need to worry, to suffer, to care. There's a certain type of comfort in knowing that at the end of it all, it's really not that important. Immortality seems to me as too many paths to a hellish existence, especially since we aren't adapted to such an existence, psychologically or physically.
This veers into the realm of philosophy but potentially almost everything we enjoy about life may be because of our mortality, even the feeling of happiness itself may be derived from knowing that tomorrow we may be dead. An immortal existence seems so different from the human experience that I can't say that it has a high chance of being a positive thing.
You can consider that a positive, but it is also an inevitability. Nobody is talking about immortality here. But you also wouldn't be saying the end of all life would be positive (which you could, for exactly the same reasons) and that still wouldn't mean you shouldn't delay it for as long as possible.
>almost everything we enjoy about life may be because of our mortality
You don't know that you're mortal until you die. It makes no difference here, because even if this were true, you are already assuming you are mortal regardless of the facts, and you will continue to do so. Being immortal doesn't imply you've also reached some state of deep enlightenment about it.
Besides, you can invert this just as well: everything we enjoy about life may be dependent upon the belief that we're not going to die soon.