I think an eternity of bliss could actually work, provided there are some radical changes to the current model of sentience we make use of, though these changes may offer some disturbing questions about free will.
But what is it one fears about an eternity of anything?
Developing a tolerance for what excites you, leading to boredom and nothing but an infinite void of time to look forward to?
Removing boredom from the equation isn't that difficult. There are times when a mind is surrounded by the familiar, but has an inexplicable sense of contentedness, a contentedness owed to nothing more than mood.
If a mood can be suspended indefinitly, problem solved. The issue here seems to be nothing more than mood. But what does one sacrifice with this restriction over mood?
Perhaps complete and total control and customization over the mood of one's self is the reward in this theoretical heaven.
Is there a reasonably plausible model for a heaven that does not cause us discomfort when we really examine it closely?
It's that pesky idea of the self that get's tangled up in my mind.
If we have a soul, do souls come out of existence from nothing? How can something come from nothing?
If we existed before we were born, why do we not remember it? Does existing still matter if we have no continued sense of self or memory?
If it does still matter, even though the current sense of self is not a factor and you're no longer "you", what's the difference between an afterlife where you're not your current self, and an afterlife where there is no more self and your cells and matter simply breaks down to be recycled in whatever material processes one would expect?
If you have some proto soul identity you only remember in between lives, that seems just as disturbing to me as complete annihilation of the self, outside of an irrational and emotional sense of satisfaction I derive that is seeded in my drive to keep on going in any way I possibly can.