Your original concern is based upon misinformation:
“The news article said that they consumed all the available sources of energy in their immediate environs and dissipated.”
(Giving your recollection the benefit of the doubt…) This is bad reporting. No one said they dissipated. The most anyone is willing to commit to is to say they have become quiescent–they are practically undetectable because they have swallowed up all the nearby matter. As matter falls towards a black hole, it speeds up and bangs around and really lights up the sky. (Quasars produce 100 times the light of a galaxy but are only 1 light-month in diameter while a galaxy is 100,000 light-years in diameter. It is assumed that black holes power quasars because no one can think of anything else that size producing that much energy.) No in-falling matter, no light show, no easily detectable black hole. So where are they? Your guess is as good as anybody else’s. Floating gently through space? Gathered up into the supermassive black holes at the center of all galaxies? (Also, your reference to “teeny black holes” translates to black holes with a mass 2-5 times that of the sun. That’s what they have detected.)
Black holes are believed to shrink through radiating Hawking radiation. (If they don’t, it poses some interesting problems for the theory of black hole thermodynamics.) It is a slow process. The only black holes that would be currently evaporating out of existence would have had the mass of a small mountain at the beginning of the universe (assuming Mr. Hawking’s rate of radiation is correct) and are called primordial black holes. The last moments of a black hole involve a spectacular outpouring of gamma rays. Searches for unexplained gamma radiation have put a fairly low limit on the number of possible primordial black holes (which in turn puts some interesting constraints on the dynamics of the big bang). Making black holes of this size and mass (supposedly) can only be done during the big bang. Only black holes from large stellar masses and greater can be made in the universe today.
Astronomers have a fair sketch of how the universe evolved for the first 300,000 years based upon research in elementary particle physics and they have a fair idea what has happened from 2 billion years up to now mostly because not much has happened (cosmologically speaking). In that time gap is when stars, quasars, and galaxies formed. What happened during that time period are guesses–but slowly becoming better informed guesses that will one day be entitled to be called theories based upon better observations and computer modelling. (To start a fight among astronomers, ask: Which came first, the star or the galaxy?)
One thing you have to keep in mind with astronomy is that it has only become a rigorous field of study in the past 50-75 years. Astronomy is handicapped by being mostly science by observation and not science by experiment.
Your description was quite sufficient. Note, however, that the Cassimir Effect is just a mechanical action resulting from the existence of virtual particles. Hold two plates really close together. Only some kinds of virtual particles can be created between the plates because of the constraint on possible particle wavelengths but any virtual particle can be created on the outside of the plates, so there is a net pressure pushing the plates together. (Which strikes me as close as you are ever going to get to a source of energy for a perpetual motion machine.)
Also, if a black hole is sitting minding its own business, it will not generate any gravity waves. Bang two together, though, and you will generate waves even humans can detect in 2003 with the LIGO observatories.