According to the Many Worlds Interpretation, there are an infinite number of realities branching off from every event in the history and future of the universe. Ultimately, this would mean that, despite your best efforts with quantum tunnelling, grey goo, and tearing the universe limb from limb you would always fail. This is because, every time you tried to destroy the universe (or every time the universe came to the point of destruction), it would branch into at least two realities, one of which would contain a reality in which you failed. Seeing as the reality in which the universe did end would also contain a dead you, you would only be able to exist in the universe in which the universe didn't end and you survived. There might even be universes out there in which you tried to end the universe, but the grey goo just ate you/you quantum tunnelled up your own arse/the person running the simulation deleted you before you got to the plug, and the rest of the universe just kept chugging along as though nothing had happened, meaning that you super failed. An infinite number of times. This also means that all of these things have already happened, in a different reality, and we're all sailing through our own untroubled version, blissfully unaware that we're the survivors of an infinite number of cosmic catastrophes.
