Regarding the "get a test" advice, fwiw a girl I know had her baby daddy push her into getting a test done. When it came back positive, the state of Illinois gave the girl a deadbeat dad form. Just a signature on her part initiated legal action against him to collect child support, essentially sicking the state on him. Ironically, none of this would have happened to him had he not pushed for that test, or at least it would have been much harder to get sued for support. Now the state is after him, certified paternity test results in hand. He moved himself to the front of the line among the state's deadbeat dads.
So, her disappearing is not the worst thing that can happen to you. If this happens, it's a great time to start saving your money. Take that 500 bucks or so a month that you would have to spend on child support and save it or invest it conservatively. Then you will always have the money to pay if she shows up with a giant bill for back child support.