Who are you, Antonio López de Santa Anna? You sound like Mexico....in 1836.....
The US will need to trade with Texas more than the Texas with the US....
Why do you think Texans should be free to ignore their share of the debt if they decide to secede? That would be like a business partner trying to leave a company without taking his share of the company's liabilities. Anyway, if Santa Anna had been willing to let Texas leave peacefully in exchange for them taking their share of the debt, he would have been in the right.
The US will need to trade with Texas more than the Texas with the US....
Unlikely. The US would still be more than 10 times as big as Texas. The situation would be similar to our trade with Canada, which is much more important to the Canadian economy than to ours.