That is not dead which can eternal lie: the aestivation for Fermi's paradox
arxiv.org
arxiv.org
I think that the 'suicide' explaination is more plausible. When an advanced civilisation concludes that there is no eternal life, that there is no ultimate meaning to life and that life always comes with suffering, it might decided that the best solution is not to produce more offspring or commit active suicide.
The suicide option is ridiculous, but I am happy to entertain it.
Better yet: any physical form of any sufficiently advanced intelligence is immediately recognized as fragile and thus existence is virtualized as fast as possible and thus equivalent to say become electromagnetic in nature.
The electromagnetic space is able to be explored infinitely more with less thermodynamic requirements than meatspace.
Then again...