Ethereum can only fail by itself
Nevertheless, there is a scenario where Ethereum could lose a lot of influence. If the upcoming change from Proof-of-Work (PoW) to Proof-of-Stake (PoS) causes significant problems and the network is no longer functional or secure enough, developers will resort to alternative platforms. This is where Cardano would perhaps come into play again. At present, however, the niche of smart contracts is more or less occupied, even though it still holds great potential for growth.
Moreover, the status quo of Cardano is not as promising as it might seem. There is not yet a single application running on ADA. Although there are already many partnerships and apparently a lot of interest, nothing is running on Cardano at the moment. Also here, problems will arise in the course of time, which have to be solved first. These are partly complex code, which also contains human errors that only become apparent during operation.
So Cardano still has a long journey ahead of it, but to speak of an Ethereum Killer already is much too early. Before that, ADA has to prove itself and Ethereum can't solve its problems. Only then there is a chance to push Ethereum from the Smart Contract Throne. Until then you should not be hyped unnecessarily and wait and see. We are curious how things will go on and will keep you informed as always.