If the universe can be evaluated in a simulation, then the computer carrying out the simulation is not actually necessary. In fact, even defining the rules of the universe is not necessary, because the contents of the universe with any given set of rules are not changed by the act of writing the rules down. Mathematical truths are true, even if they're never discovered. If a universe can be simulated, then it has a mathematical description, which means all of its configurations, and all of the events within it, are determined from the mathematical description.
(As an inhabitant of the universe, you may experience non-determinism, but this is because you are limited to experiencing one path at a time. For example, you can make a mathematical model of the outcomes if you flip a coin 20 times in a row, and even though the outcome of any given path is non-deterministic, all of the possible observations are determined purely by the rules, and all are equally true regardless of how many times you flip the coin, or whether you even bother flipping the coin at all).
By analogy to Conway's game of life:
The outcome of any given configuration in Conway's game of life is fully decided regardless of whether anyone actually runs the simulation, regardless of whether anyone writes down the rules, regardless of whether anyone even thinks of the rules. The outcomes of Conway's game of life didn't become decided at the point that the first simulation was executed. The outcomes were always there.
No observer inside Conway's game of life has an experience or lack of experience due to the simulation being evaluated on a computer. Evaluating the simulation has no effect on the outcome. Evaluating the simulation allows someone outside the simulated universe to inspect its state, but it has no effect whatsoever on the observers inside the simulated universe. They were there all along.
The observations made by observers inside the simulated universe are decided by the specification of the universe, and are the same regardless of whether there is any computer outside the simulation actually evaluating it.
All of this is to say that IF our universe can be simulated, then we don't need the simulator. The fact that it can be simulated is enough to create all of our experiences. And in fact I think this is the "true" explanation (whatever that means) of why the universe came to be: we exist just because mathematics says we can. (And, further: every possible universe "exists" - as far as the observers inside it are concerned - and every possible experience is experienced).