Perhaps we can look at this another way. The materialist model of reality is grounded in observation, is it not? One must observe a phenomenon in order to study it scientifically. Therefore, this perspective is fundamentally tied to the act of observation. How then do you propose to study "the universe" defined by a lack of observation? To say, "I am going to scientifically study the universe as it is in the absense of an observer" is absurd. It can't be done.

Instead maybe, you would like to deduce the state of the universe in the absense of an observer using logic and math. This isn't viable either, since here you are, still observing, just with different tools. Not only that, but whatever it is you come up with is even more of an illusion than what you might observe in the present since all of the logic and math exists only in your own mind, and I think with a little introspection anyone can come to realize that fact.

When all of your knowledge of 'what is' is dependent on not only "the thing" but also yourself, removing yourself obliterates the knowledge. The illusion is the perceived ability to know "the thing" when in reality, all you know is your knowledge of "the thing". The thing, which is all of the universe, is fundamentally outside of you, and yet your perceptions of the universe are fundamentally inside of you. They are forever seperate.

You can say that without an observer the universe persists, but this perspective is not compatible with the scientific method since science requires an observer in order to study phenomena. Scientists do not speculate about the existence of something that they cannot observe, so why then would a philosophical position based on science choose to speculate?