it will exist forever, since it already made its fame, maybe after a while (at least 5years), its dominate possition is going to be replaced by other coins. But I do not think that can make bitcoin die out shortly.
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I do agree with what you have said that it will last.
But this will only happen if and only if there are people who will still put their confidence over it.
Cryptocurrencies status is dictated by its users and may be gone anytime if this users will chose not to use it anymore.