Sounds about right. Cornyn will lose only inner city Dallas, Houston, San Antonio, and the Rio Grande Valley.
Cornyn comes from San Antonio and in 2002 he carried Bexar County 51%-47%.
Given that he barely won the county, he'll probably lose the inner city. He's a Republican, after all.
The inner city has never been Republican-friendly to put it mildly. His bump in Bexar County was probably about 3%-4% in 2002 (best guess).
Also, a Democratic candidate would also win El Paso, the Beaumont-Port Arthur area, inner-city Austin (obviously) and if he's particularly strong, some parts of east Texas. Democrats would do ok in the inner suburbs of Dallas and Houston (and probably Austin as well).