We know from geology that the plates have been seperate and moving around (colliding here, spliting apart there) for most of Earth's history -
certainly way before the Chicxulub impact that contributed to the demise of the dinosaurs. Although most people have heard of Pangea and know it was
one single large landmass that existed during the age of dinosaurs, there have actually been at least 2 earlier occasions when all the continents
formed one single landmass, before subsequently breaking up, drifting around the planet, and ultimately rejoining. In a hundred million years or so
it's predicted that most of the current continetes will have again rejoined into one big super-continent.
The break up of Pangea started with the the northern part - Laurasia - seperating from the southerm - Gondwana. Subsequently the Americas each
individually split away from Europe and Africa. The Chicxulub impact (in central America), as well as occurring long after this had all started, is
also in the wrong place to have caused it.
If a major impact did cause Pangea to split up, we have as yet to find any evidence.
However, some geologistsdo speculate that large impacts may affect the movement of individual plates and even possibly cause the creation of a rift in
a plate which may eventually leads to it splitting into 2 seperate plates.
Unfortunately we still don't know enough about the mechanism that causes plates to move to be sure on this.
But your idea isn't entirely implausible
