The first question doesn't really interest me inasmuch as living to a very old age on the order of hundreds or thousands of years is simply not a live possibility for anyone. The second question is much more interesting since life after death is a very real possibility for everyone.
In posing the question Fischer seems to rely on a popular conception of what sort of life is rewarded by eternal immortality. He says this:
But let’s abstract away from details. In all plausible religious views, what matters crucially for your prospects after you die—your next life in the wheel of reincarnation or your place in heaven, hell, or perhaps purgatory—is the moral quality of your life here and now. That is, your prospects are enhanced by right action for the right reasons in this life. You need actually to care not just about yourself, but about others—you need to love others and to care about justice. If your actions manifest love of others and a dominant concern for justice, then you will be rewarded in the afterlife.Now I don't strongly disagree with this, that is I do think love and justice are the two absolutes by which we are commanded by God to live, but it's possible that there are people who live by these absolutes who nevertheless despise the God who ordains them. On the Christian understanding of eternity, heaven is established as a "place" where we live forever bathed in the love of God. For those who reject God's love, who are hostile to God, eternal life with God would be hell. Each person has to choose whether they desire to spend eternity with God or not, and I suspect our attitude toward God in this life serves as our choice.
It is key that you must act for the right reasons. And here it is important that the reason for your behavior must not be that it will enhance your prospects in the afterlife. You may of course understand and anticipate this fact. But it cannot be your reason for action. If it were, then your action would be motivated by self-interest and not morality. You would not be doing the right thing for the right reason. So there is a sense in which your behavior now should be focused on this world and the needs and interests of others here and now, even if one were to believe in an afterlife.The right reason for loving others is gratitude to God for what he has done for us in securing for us eternal life. We love others because we love God, are thankful to him, and want to do what God wants us to do. And what he wants is for us to love the people he loves.
If our love for others is based on self-interest, or grows out of the kind of personality we're born with, or is based on fear of punishment, that love, by itself, is not salvific because as Fischer says it's not based on the right reason. The right reason is a love for God, at least that's the right reason in the Christian tradition.
If this makes sense it may prompt the question of the fate of those who don't love God. I'll share some thoughts on this in a day or two.