Boeing is going to about a year late delivering their first tranche of KC-46s and the penalty will be..... good question. The contact defines no penalties for schedule slippage or late delivery.....
It's a firm fixed price contract. For a development program. McCain supposedly loves those and even wants the super stealthy LRSB development to be firm fixed price! Boeing has already absorbed billions in overrun costs and will absorb more to resolve these latest issues.
And FWIW, the late deliveries will result in a contract breach which will trigger a schedule rebaseline negotiation and its during those negotiations that Boeing will find out how much this will cost them. And although Boeing will (probably) deliver the physical aircraft on schedule, they will be non conforming in that the refueling system will not be certified. The software update that will make the aircraft conforming will be installed after the aircraft are delivered. So depending on what USAF had originally planned to do with the aircraft those first five months, there may be little or no impact to USAF. For example, if the first five months were planned for basic flight crew training with little or no aerial refueling, USAF's schedule is minimally impacted, which (theoretically) should result in a smallish penalty. Boeing have to wait and see.
Still plenty of real-estate at Mobile, Alabama should the USAF decide on some 'interim tankers'. Kinda like they did when the Lockheed L-193 was the preferred tanker in 1954, and the Boeing KC-135 was brought in as an 'interim tanker'.
Something tells me that buying Airbus A330 MRTTs at this late stage as an "interim" solution will take far far longer than the five month delay in KC-46 deliveries. And the "interim" KC-135 became permanent largely because Boeing was able to deliver their tanker well ahead of Lockheed. And any airplane Airbus could deliver would indeed be an MRTT and
not a KC-45 so like Boeing's airplane, nonconforming.