I don't think anything will last forever... But there are two ways blockchain might die:

• If every single computer running its nodes stopped somehow, or was cut off the internet. That's unlikely, but who knows what'll happen in the future.

• If some new technology made the blockchain's encryption methods obselete. Like making hacking users passwords for HIVE trivial. If no hardfork came to solve it, the blockchain will die. Even if a hardfork came to solve it, the damage might be already done to many user accounts making the blockchain lose its value.