I'm Back
After finally getting through to an executive complaint hotline regarding our dissatisfaction with the 1-week response time Comcast told us to expect, a technician came out to the house yesterday.
It turns out our sprinkler guys had cut a cable, but we couldn't tell since Plano is one of the few cities still using a two-cable delivery system. We still had TV, but no Internet. The technician was polite and had the problem temporarily fixed in less than an hour. A crew will come out in the near future to bury the temporary cables (which are currently running across the surface of the lawn).
Long story short, the outage was our fault. Apart from dissatisfaction with the initial response time, Comcast handled the situation great.