You obviously have to suspend disbelief on either Death Star crashing to a planet/moon and not rendering the whole thing uninhabitable. I've read a couple of
fan theories calculating mass, impact, etc. that describe the result.
There were comics that described most of the debris getting pulled in to a temporary wormhole created by the exploding hyperspace engines and thus saving the planet.
Either way, its all scientific BS, but sure as heck looks cool in the trailer and I can't wait to see what its all about.