Some altcoin will take the throne if bitcoin doesn't change. Things change... deal with it or be pushed out of the way. Pigs get slaughtered.
And Litecoin will most likely be a new king of crypto
Regarding the noise raised by the OP, I have heard many people claiming here that miners have been screaming for years about the necessity of the blocksize increase. If it is really so (I don't know, but let's assume that) and the blocksize increase was (is) as urgent and pressing as they have been screaming, what prevents them from introducing this change on their own (given their hashing power monopoly)? Okay, some dudes would be quick to retort that they want consensus and all that but if there is no consensus may be the bigger blocks are not in fact so urgent as these miners are pretending them to be? As I see it, you can't possibly have it both ways
Litecoin is just shifting the issues of Bitcoin, it runs on the same technology, just with a different algorithm. The algorithm was once chosen because Litecoin-Developers saw the issue with centralized mining by farms running on ASIC. So they thought Scypt would be more ASIC resistant, which became untrue in 2014. Litecoin will cause the exact same mining farms once it becomes valuable enough.
As long as none of these coins switches to PoS, the issues will never be solved, and we continue wasting energy on artificial complicated math puzzle that do nothing but proof that someone who claims to have made a block wasted some energy to do so. And soon a few huge farms will control the blockchain and decide with their hashpower the politics of the coin.
The issue in PoW remains that the miners are not necessarily the users of the coin where PoS makes sure that these that create the block also actually own the coin and have put investment into it. PoW miners can mine, dump and then forget the coin and if everything crashes, they can still sell the hardware and move on, while attackers on a PoS-system jeopardize their own wealth.
And for the other theoretical attack, it's only a matter of the network hashrate how secure it is. To attack a PoS Bitcoin with the same marketcap of Bitcoin today, you would need more than 20 billion USD (probably even much more, since the mere attempt to buy 51% of the coins will increase the price astronomically). To attack a smaller coin that secures with PoW, you'd need a few million only, nothing someone like a secret service couldn't afford, especially when, as said, the attack doesn't directly attack the wealth you had to afford to gain enough power over the blockchain.