For Houston specifically KTRK ABC 13 will remain with Disney. Also Disney will keep the ABC affiliation for their O&O's like KABC/WABC/KGO/WLS. Note no duopoly will take place between ABC and Fox since the Fox Owned stations like KTVU, KTTV, KRIV and WNYW were not included in the Disney deal.
The intent as far as I was aware of was that the Fox Television Stations division wanted to go after Sinclair stations in some parts of the country and remove the Fox affiliation in Sinclair/Tribune markets and place the Fox affiliation somewhere else in those areas.
For Disney the reason for the Fox/disney deal was to go after Netflix, YouTube and Time Warner for content.