Five billion years is a veeeerrrrryyyyy big period of the time the sun blasts we wont be surviving .and every star dies some nor the other we should stop worrying about it and rather can focus a bit on will the earth be effected by it.we really have so much time for this.if it states that earth will be effected ,then we could start doing something to save.
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As u know that sun is also a star and every star has its own life time and sun is an young star it is just an estimation it may last for even longer time .

sun have its own lifetime the scientists have found that  it will last for 5 billion years 
it is just an estimation

we should not worry about it as it takes billions of years we will not be there at that time
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