FTB, there have been several posts regarding "what happens to the break if there is MX, weather delay, IROPs, etc."
The FAR 117 section is very clear that in order for the airline to conduct Split Duty Ops, they must meet all 6 requirements of FAR 117.15 and one of those [117.15(d)] specifically states:
In other words, if your rotation was built to have a 6 hour break, and WX causes you to arrive 2 hours late, then they are going to have to slide the departure time of the morning flight by two hours or find someone else to fly it.
Furthermore, 117.15(b) requires that the break doesn't officially start until you actually reach the "suitable accomodations" so if you are having trouble getting the hotel van at 0100 in the AM, your break doesn't start until you arrive at the hotel. Lastly, one of the requirements of Split Duty Ops is that the rest Period be provided in 'Suitable Accomodations', so even if you wanted to just stay on the airplane overnight, you'd be busting the FARs.
It should be noted that the only thing we have so far from the MEC in writng regarding Split Duty period ops is this:
FAR 117.15 only requires a break of at least 3 hours, so any break at Delta would have to be at least 3 hours, though the rumor floating around is a contractual minimum of 6