The idea that the planet was physically destroyed, Death-Star-style, is not "likely" at all. The Ur-Quan have never evinced this level of power, nor would that kind of overkill be necessary -- there's nothing about the physical existence of a planet that says that a particular kind of species must evolve there. After all the Dnyarri were killed or changed into Talking Pets, there's no reason to think Glilandy wasn't left as a lifeworld or, at *most*, scorched away into a deadworld. But the idea that the Ur-Quan have the power or the propensity to actually blow up planets is silly.
Also, much of this info belongs in the Dnyarri entry, not the Glilandy entry.
...No power to wipe out the planet, huh? Death-Star-style, huh? ...Ever heard of the Sa-Matra?...
Yes. The Sa-Matra blows up enemy ships. Have you ever seen a single reference to it blowing up planets? (Do you know how much energy actually blowing up a planet entails? One of the least realistic parts of Star Wars -- to impart enough energy to a planet-sized body to blow it apart into pieces that don't immediately slam back together under the force of gravity would require more energy than our sun emits in a day.) The Sa-Matra is powerful because it has very long range and can pick off enemy ships from a distance without fear of reprisal, not because it has unlimited amounts of firepower.
The most powerful weapons in SC2 are the Precursor Bombs, which are explicitly said to be "planetary engineering tools" yet are only powerful enough to break apart a "small moon" (probably Phobos-sized) or "make a big crater" in a planet. The Bomb still had to be enhanced by the Vindicator's systems before it could blow up the Sa-Matra -- which is far smaller than a planet. And the most destructive event we've seen, the Shofixti Ultimate Glory Device made from a Precursor Bomb inside a sun, only created a massive flare of radiation that *killed* everything on Kyabetsu but far from destroyed Kyabetsu.
Destroying a planet is something that involves titanic, impossible amounts of energy and would be a thoroughly useless thing to do in almost any situation -- wars are fought between the people who live on planets, not between the enormous hunks of rock themselves. They don't need the power to blow up planets any more than we need the power to level mountains -- in both cases all we need is the power to blow up cities. "Blowing up a planet" is a trope from the rather sillier kinds of science fiction because it looks and sounds cool, not because it's at all realistic.