Of course the Dems will change the rules. Gabbard isn’t as controllable as Biden and the DNC thinks it has already defeated Sanders.
Regardless of which ancient white guy gets the nomination the real person to watch out for is the VP the DNC will foist upon the nominee. I could see Biden resigning once he exceeds W.H. Harrison’s tenure and enjoying retirement and the perqs of an ex-president. Of course, if Hillary is the VP he should resign right after being sworn in. If Michelle is the VP he will probably wait two years and a week so Michelle could run twice on her own.