If they are at fault, you have zero liability. Do not file a claim with your insurance, because you will have to pay a deductible if you do.
<as always, please remember that the at-fault insurance company is not your friend and their job is to pay you as little as possible to close out the claim. They are a business, and you are nothing more than an expense to them.>
Um. That all depends upon the State. Many States with No-Fault insurance pretty much always has one going to their own insurance company for the organization of getting the car into a body shop and repaired; the checks to the body shop come from one's own insurance company.
However, we all scream, "What about the deductible!" Answer: One's own insurance company, complete with lawyers on
your side, goes after the at-fault driver's insurance company. When they pay up, which they do, you get your deductible back, your insurance company gets reimbursed for its trouble, and all is good with the world. This has happened to me. And, in the case where the perp was not insured or was under-insured, one's insurance (in a no-fault state) has a rider specifically for that.
I've lived in Massachusetts, NJ, and CA (briefly), all three of which were no-fault states, and that was how it worked. The one time I got rear-ended in Indiana which, at the time, was
not a no-fault state, getting the perp's insurance company to pay up was like pulling teeth. Essentially, the crowd there (back in the 1980's, State Farm) had the attitude that if I wanted paying, then I was going to have to engage a lawyer. (They knew I was a starving college student and couldn't afford neither a lawyer nor the time to go after them properly, and were taking advantage of the fact.)
And that's another thing about States that don't have no-fault: The legal profession in those states tend to oppose no-fault with a burning passion, since getting claims paid in those states is pretty much a full-employment act for lawyers.
Dunno the rules in Texas.