Yes - if you redefine 'exists'.
This rhetorical tactic is often done, like when someone says'everything is an illusion' just redefines illusion. Existence has an accepted context, a use, it points at distinctions in certain language games. In that sense, no.
I suggest the way to think about taking measurements and what exists where, is Indra's Net. Each point in the universe contains information about other points, we are each mirrors reflecting other mirrors.
It is a mistake to think quantum observers have to be a conscious sentience. You might be interested though to look at Conformal Cyclic Cosmology, in which theory something like what you mention happens: when there are only photons left, which don't experience time, a large high entropy universe becomes conformally equivalent to a small low entropy universe - a Big Bang.
More generally, what you are talking about is just the Quantum Multiverse, in which all possible outcomes from our same initial conditions exist, and each branch is experienced by the minds on it as their only timeline, and we are one of the timeline we are on's necessary subjectivities. But in the Multiverse as a whole, all the outcomes are there.
This is a statement of the Wavefunction of the Universe, the idea that measurements don't divide timeliness, but only add a specific sub-outcome to a bigger outcome, both of which are quantum wavefunctions.