If a changing fell into a pool of
this stuff, would the universe collapse into itself?
Given that the Star Trek universe has survived an event that should not be possible even by its own fast-and-loose interpretation of Berman-era Jet Propulsion Lab notes (to wit, a supernova's blast effects both travelling at multiwarp speeds
and gaining energy as it expands), I don't think so. However, you do raise a valid question that even the Relaunch Novels (now relegated to something called the "First Splinter Timeline", and blamed on the events of
First Contact) never fully answered....
It has been revealed in audiovisual canon that the preponderance of humanoid life in the Milky Way was due to DNA distributed onto developing worlds between 3-4 billion years prior by an advanced progenitor culture. (Presumably, if the Revolt Against the Thrintun and the resulting mass death of sentient life happened at the same time in the Trek Universe as it did in Larry Niven's Known Space (ref. TAS' "The Slaver Weapon"), these worlds were the recipients of extremely good timing.)
In the DS9 Relaunch Novels, while Odo undertakes efforts to reform the Dominion using particularly flexible-in-their-thinking Vorta and Jem'Hadar, the other Founders attempt to search for their progenitor. When they discover a possible candidate dead from lethal radiation, the Great Link breaks apart and scatters, leaving Odo (who goes back to the Alpha Quadrant in 2383), Laas, and 2 others of the hundred changeling youths that had been sent out decades earlier in charge of the Dominion.
Anyway, the similar abilities of the Delta Quadrant's Silver Blood might well interest the Founders, and there may be a link (pun not intended) in common which could point to a similar galactic ancestry akin to that of the "solids". As both of these came out of TNG spinoffs, it's unlikely that Old Man Picard (the show, that is, such is what I call it) will pay much attention to such notions, but what's fandom for if not to spin such ideas?