If you're asking me to show that an afterlife doesn't exist, I can't.
I know you can't and that's my point. If an afterlife does not exist then this truth can never be demonstrated to anyone, thus my point that it seems irrational to believe that an afterlife does not exist. This is not the same as asking someone to prove unicorns exist, because unicorns very well could have existed at some point in the past. An afterlife only exists after death, it can't possibly exist in the past, it can only exist in the future.
If an afterlife does exist then this truth would only be demonstrated after you die, thus proving its true at that point in time. I'm incapable of proving that an afterlife exists, but after death it would be proven. This is why I claim to have a rational belief in an afterlife.
Maybe a different definition is required of what it means to die.
Romans 6:3
"Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death?"
Philippians 1:21
"For to me to live is Christ, and to die is gain."
2 Corinthians 5:17
"Therefore, if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come."
1 Corinthians 15:31
"I protest, brothers, by my pride in you, which I have in Christ Jesus our Lord, I die every day!"
Matthew 10:38
"And whoever does not take his cross and follow me is not worthy of me."
John 12:24
"Truly, truly, I say to you, unless a grain of wheat falls into the earth and dies, it remains alone; but if it dies, it bears much fruit."
Mark 8:35
"For whoever would save his life will lose it, but whoever loses his life for my sake and the gospel's will save it."
Galatians 5:24
"And those who belong to Christ Jesus have crucified the flesh with its passions and desires."
Galatians 2:20
"I have been crucified with Christ. It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me."
The consistent message that one must die to self in order to attain life is at least interesting to say the least.