While FCA US (aka Chrysler) would never want to give up the Cummins B, they have a marketing problem that could force their hand.
Diesel engine option price for 2017:
Ford F-Series Super Duty: $8595
Chevy/GMC Silverado/Sierra HD: $8995
Ram 2500/3500: $9100
Cummins is the most expensive, but the bigger issue is this... Ford and GM give you the max hp/torque rating across the board (3/4 and 1 ton), with no extra charge for the transmission that can handle it. You pay nothing for the Ford 6R140 or the Allison 1000. Ram is a double whammy in that to get the top rating, you have to first pay for the (slightly) more expensive 3500, *and* you're charged the extra $2695 for the Aisin AS69RC.
So, Ram is charging $11,795 for 3rd place in torque, where GM charges $2800 less, and Ford $3200 less. The Powerstroke and the 6R140 are 100% Ford, and GM is the majority owner of DMAX Ltd, - so FCA NV may be thinking the Fiat/IVECO engine may be cheaper to price against the competition's in-house offerings. FCA NV may feel an in-house engine can be priced more competitively, but they'd still have to get a new transmission... either a 69RFE, or something that can be acquired where no extra charge needs to be passed on to the consumer.
So if you want the Cummins to stay beyond the current contract, tell FCA - both US and NV - you don't mind paying (notably) more for it. I won't be in the market for a new rig until the redesign (moved to a new place this year and have to pay those expenses off first), but if I had to buy a new truck in the next 12 months, cost effectiveness isn't quite with Ram right now - for me (your mileage may vary, of course).