So far, Bitcoin is considered sustainable, secure and difficult to destroy, but it is still threatened by risks such as 51% attacks, quantum computers or protocol vulnerabilities. While these have never happened, it is clear that these are potential risks that bitcoin could face and we cannot deny that. So, to be fair, it's still too early to say that bitcoin is immortal.
Also, bitcoin was created after the 2008 financial crisis and so far the only crisis it has experienced is the covid pandemic. It has never experienced and faced devastating crises like world war or the great depression (1929-1933), 2008 like what gold has experienced. So there is not enough data yet to assert that BTC will be immortal if suddenly the world experiences similar things.
"Immortal" in the sense that the source code is widely distributed across cyberspace. Even if the main Bitcoin blockchain is shutdown (which is very unlikely to happen anytime soon), anyone can "relaunch" it by using an improved version of the source code. But you're right that external attacks remain a high-risk target against Bitcoin's network security. Nothing is 100% safe and secure against external threats.
At the pace Bitcoin is progressing, I'm sure developers will come up with a solution against Quantum Computing attacks. The chance of a double-spend attack in the future will be slim as more miners (hashrate) join the network. We can't predict what will happen in the future, so let's hope for the best.