And how long would it take for Texas,standing alone,to be absorbed by Mexico?
I can't tell if your asking seriously. I suppose a major episode of glaciation could tip the scales in Mexico's favor.
The opposite is more likely the case. That is, for an independent Texas to start absorbing chunks of Mexico, eliminating the gangs from their annexations before pumping them full of prosperity the likes of which they have never seen.
All the while, the remaining Mexico would be in a situation of reform itself or die. This would mean finally discarding its “Old Europe Disease” of a hyper wealthy pseudo nobility families lording it over the peasantry.