I'm not sure I understand what you are trying to say, juvenissun. So, maybe I'll just try to express my own take on the subject as thoroughly as possible:
1. Biologically and ecologically speaking, death is an integral and important aspect of life. Without death, we would literally consume ourselves, unless of course we abstained from ever producing (equally immortal) offspring. Death is not the enemy, but the motor of change, which in turn is the very essence of life.
Maybe future scientific discoveries will make it possible for us to retain our youthful vigour for vastly extended periods of time, retaining the physical fitness of a 20-year-old for hundreds of years. This will create all sorts of societal and ecological problems, but given the typical trial-and-error, mankind will either adapt to these changes in a fashion that is sustainable - or it will disappear from the face of the earth. Indeed, we may become the first species to consciously influence or even control our own evolutionary path, as opposed to just being jumbled about in reaction to external influences creating pressures. But even then, death will still be with us in one form or another. It's simply the most fundamental process of transformation, and without it, everything would be stagnant and sterile, like a chemical equilibrium. Life is change, impermanence, transformation.
2. Meaning and purpose are ideas that, for the most part, we imbue our own lives with. Of course, this can happen on many different levels, from the societal to the personal, but in the end, it's all about what we project into our own existence. As beings who are capable of premeditation and reflection, these purposes are rarely restricted to momentary, instant gratifications, but take the consequences into account. Even creatures of mere instinct shrink from that which would endanger their survival, and the same holds true for ourselves.
Thus, it would be foolish to equate happiness (that is, a feeling of serenity and fulfillment) with pleasure (that is, mere positive stimulus) - although the former can include the latter. For example, if I were in the desert, it would be quite pleasurable to take my supply of water and dump it over my head, as the cool shower would feel wonderful in the stifling heat. It would be absolutely detrimental to my life (and thus, my happiness), however, as it'd pretty much mean that I'd die of thirst.
3. There are individuals who derive happiness from acts that are detrimental to others (and, ultimately, themselves). However, the problem of evil is not metaphysical in nature - it is pretty much a mundane and altogether human concern. Moralities are cultural constructs that rely (at least partially) on social impulses that have been with us since before we gained self-awareness. And these impulses are ultimately tied to the plain necessities of surviving as a group - that's why we don't tend to feel too good about people whose short-sighted egotism would endanger our survival (and, ultimately, their own).