If you reject that tacit assumption, you may wish to examine the closely related tacit assumption that living persons that experience do exist. The relation between the two assumptions is informative.
The thing called you is, in one model, just a collection of atoms, a particular solution to some equations, after all. Some complicated world-lines, that anyone with a sufficiently powerful computer and the right collection of seemingly random numbers could reproduce in principle - or is it?
Maybe the dead don't experience anything. But until you can say what distinguishes "experience" (and "reality") for the living from the mere existence of solutions to equations, it's a missing-definition error to conclude anything sweeping and universal about experience.
You can certainly define experience in various ways, for example particular kinds of electrochemical activity in the brain, or organised information processing in matter of a certain kind. If you do that, you can conclude that those processes cease.
But those are limited definitions for convenience. We cannot say with certainty that's what actual living experience is "made of", so we cannot say with certainty the universal statement that all forms of actual experience cease.
(We can, however, turn "certainty" in the above into a kind of variable, in order to understand what we mean more subtly.)
The distinction is sometimes called "fire in the equations". Who knows what makes a living person actually experience - assuming you believe living persons do.