Even with a Mexican win, it would still have to deal with a Texas that is being culturally and demographically "converted", laying the seeds for future secession during political turmoil. In 1830 there were 7000 Anglos + slaves in Texas, and this was concerning enough for Mexico to abandon the empresario foreign-immigration system for Anglos. By 1835, there were 35,000 Anglos + slaves. This is not counting the Native Americans that are being driven into Texas by Andrew Jackson and Comanche expansion.
The conundrum for Mexico in Texas was this: the native 2.5k Tejanos simply could not provide basic border security from bandits, filibustering attempts, Comanche/Karankawa/Tonkawa raids etc, meaning a constant drain of dollars from other regions into this very peripheral area. If Texas was to defend itself (and Mexico) on its own dime, then some immigration had to be allowed to spur economic development - which, given the US' proximity, meant turning the region Anglo. EVEN if OTL Mexico was able to enforce its ban on US immigration, the proximity of Texas to New Orleans would have linked the former's economy with the latter anyway, creating the conditions for eventual secession.
So IMHO, the most realistic way for Mexico to keep Texas post-San Jacinto is to keep the region underdeveloped - no immigration, no economy, and the central government