Yes, you may extend your TN status by having your employer file and I-129, or in the alternative, you can request another TN visa by going through a border checkpoint. Be advised, however, that the management consultant category is looked upon with suspicion and you should tread carefully. I have gotten many "renewals" in this category, and it was never easy or cut and dry.
Classifying an employee as an 1099 independent contractor is a common way for a company to avoid paying taxes, benefits, and overtime. However, there are strict rules on the application of this classification. I would most definite consult with an attorney about your situation.
The answer to your last question is yes, your employer can sue you. Will he/she prevail is a different matter.
That being said, I agree with the other attorneys that non-compete and non-solicitation agreements are generally unenforceable in CA. That should give you a good idea of what your legal rights are.
The bottom line is that there's no use worrying about what your employer will do or not do until it happens.
Even though your mother left the country in 1996, and the 10 year unlawful presence bar has run its course, some consular officials routinely require persons with any accrued unlawful presence to apply for a waiver when applying for any type of visa.
Based upon the limited facts that you presented, you should be able to sponsor your mother for a green card. However, you should enlist the help of an immigration attorney because your case presents many complexities.
You did not discuss why...
If you file an EEOC claim and your employer takes any adverse employment action against you (e.g., demotion or termination), you will have a good claim for retaliation. A retaliation claim can survive even if the underlying EEOC claim is found to be without merit.