What fate is there to talk about? If it's true that matter cannot be created nor destroyed, the patterns of science will be unchanging. It'll continue endlessly, scientific events constantly occurring, all of it adding up to nothing.
If the law of conservation of mass is false, however, then over time, all particles in the universe will decay and eventually, the universe will become an empty void. Anything after that is not part of this discussion, since the universe you refer to will have ended.