In Texas, if your property is foreclosed on, the lender has two years to sue you for what is called the "deficiency" or the "deficiency balance." If they sue you after that, you have an "affirmative defense" to the lawsuit, and you should hire an attorney and fight it. See Texas Property Code, Section 51.003.
Not only that, but if a lender or mortgage servicer sues you after the statute of limitations has passed for them to sue you on the claim, you may even have a claim against them for violating the Fair Debt Collection Practices Act or the Texas Debt Collection Practices Act. Again, consult your lawyer about it.