Should an Officer who was non-selected for promotion, and discharged at 16 years of service, reenlist to finish their 20?

There is absolutely no right or wrong if the officer decides one way or the other. Its strictly HIS opinion and decision.

Yes, of course they should.

No need to re-enlist to achieve retirement benefits. Keep your commission and stay in the Army Reserve. Find a position in a troop program unit (TPU) that will support your MOS. You are more likely to find such a position in one of the training divisions. You want to find such a position in a unit like 75th Division (Training). This is a reserve unit that contains officer/NCO teams of all different branches of the service. The unit's mission is to train Army Reserve and National Guard Battalion and Brigade staffs through innovative exercises and computer simulations. You can easily accumulate the 60 points per year you need to get a good year in, and likely be able to remain until you hit your MRD. Further, there are ample opportunities there for extended schooling and additional Active Duty for Training (ADT) that would enable you to obtain up to around 120 points per year. It you have completed your OBC, and OAC you'll be quickly promoted the grade you missed while on Active Duty (assuming that was Major). You will be able to attend CAS3 and CGSOC through the Army Reserve Schools that are out there as well (and you can also get retirement points for that as well whether or not you receive pay for them, although you will receive pay for the ADT portions of those schools anyway). I was in a similar position as you and did what I advise, although I did not immediately jump into it. I draw something like a 35% retirement check as a result. Jump into this NOW and you might still get close to a 50% retirement check since you already have 16 years. Units such as the ones I suggested NEED the experience you have as many of these teams are run by guys who only attended OBC and then went straight into the Reserve/Guard. They have book knowledge, but not any real experience. You have both.

Yes; for the pension and retirement benefits, especially during this time of difficulty attracting/retaining service members. Or, see if another branch will accept him/her as an officer.

Why not?
My last battery commander in Germany failed to make Major and was separated. I heard the rock in his rucksack was education, not to mention he had a load of family problems, such as a daughter with MS. I wonder if it affected his duty performance. When he got to our unit he was pretty much a broken man, I ran into a guy who'd served with him in Nam who spoke highly of him. He called him one of the best officers he'd ever served under. I got shanghaied into being his driver my last Graf and there were times we'd be sitting in the jeep late at night talking and I'd see traces of the guy the fellow described. Sad. I don't know how it turned out for him, I do know he left the service.

I'd never thought he might have the option to turn around and enlist and finish his career.

I came in at the tail-end of the Vietnam Era. There were literally thousands of officers who ran afoul of the RIF (Reduction in Force). I recall reading somewhere there were close to ten thousand or so chopper pilots alone sent home - just to have a shortage in the early 80s.

For many captains the choice was to take the RIF (there was a cash kicker involved depending on Time in Service and base pay) or take a reduction in rank to SSG E-6. I knew several NCOs who had taken the demotion to finish their retirement. I know it had to sting, but...

In the 82nd DivArty in the early 80s the DivArty S-3 (or AS-3?) was a Major who was one of those guys who'd make you want to buy your own beer. His Operations NCO was an older MSG who was one of the greatest guys you'd ever want to meet.

I learned the backstory behind those two. It turned out the MSG had been the Major's battery commander in Vietnam when the Major was a new Lieutenant. The MSG had gotten caught in the RIF (again, education) and taken the reduction to SSG. In the intervening years he had risen through the enlisted ranks to E-8 and the Airborne Community being what it was back then (the old "Airborne Mafia") had found himself working for his old lieutenant. There was an interesting chemistry between those two.

Another case was when I was working S-3 with 18th Field Artillery Brigade (Abn) when it was still XVIII Abn Corps Artillery. Our MSG/Operations NCO was another former officer who had come down on the RIF and taken the reduction to SSG/E-6. But he'd been smart and managed to retain a reserve commission. Every year he would go on his two weeks active duty as a reserve officer - I'd always wondered about the administrative side of that - whether he had to take a leave or what. The thing is , he'd not only worked his way up through the enlisted ranks, but he'd gotten promoted in the reserve to the point his reserve rank was Colonel.

The year I was with the Brigade (I transferred to the 82nd that winter) he did his Summer training at Bragg; one of the NCOs said he did that every year. He got a kick out of coming into the shop in a Colonel's uniform and having his boss, a Lieutenant Colonel call him sir.

It's a funny thing, the day I was medically discharged from the Army for my injuries I went to visit the 82nd Abn Division Museum one more time before I took the uniform off for the last time. I pulled up to see his retirement ceremony; he'd made Command Sergeant Major. I was able to hang around and shake his hand. I've often wondered what his reserve rank was when he retired. This was 1987.

But yes, I'd finish my time - perhaps you can keep a reserve commission. I don't know what the regulations are these days.

In my batallion there is an E6 who was a former Major in the navy. He left the navy & then came over to the army enlisted. So I would say it's legal & yes. It's their career. As long as the regs are upheld & met why wouldn't he. Seems weird but oh well.

Yes you schould. You are 3/4 there. So just finish the mission. The health care is worth it in the end.

Yes, shouldn't have been discharged.

As Major G stated why give up a retirement check? I worked with an Army aviator Major who I heard was passed over for a promotion he was gone for a few months only to return as a CW2. He would then be allowed to stay in the Army as long as he gets promoted to CW3, CW4, and so on but still retire as a Major.

Absolutely, I had a commander who passed over (long story, he had failed a unit within a group, and a few months later he was assigned to that Group in another detachment. We had a very petty Col who screwed his evals). He reverted back to E-5 after being a unit Commander. We had nothing but respect for the guy, and we all thought he got the shaft.