You’ve done a very good analysis and may well be right. If officers are ordered into confinement, they go to Leavenworth to serve it, even if its just one day. I’ve seen several of them in that condition and they aren’t happy campers.
The closest analogy is CPT Yolanda Huet-Vaughan from the 1st Gulf War who ended up exactly as you predict in this case if my memory serves. It remains possible, however, that LTC Lakin will be allowed to resign.
As part of a pretrial plea agreement, perhaps. But, once convicted, he's toast as there is NO WAY they're going to offer some kind of suspended sentence in this case, especially considering how public Lakin has been in his contempt. He didn't just disobey command, he made a spectacle of it. Commands don't like spectacles.
For what it's worth, I think the chances of a plea agreement in this case are precisely 0.00%. I don't think it would accepted if offered, and I don't think there is ANY chance of one being offered.