Besides separation, what are the options for officers who are passed over twice?

BLUF: You can stay in to 20 years.

For Majors in the USAR, “Removal from an active status will be on the LATER of the first day of the month after the month in which the officer completes 20 years of commissioned service, or the first day of the seventh month after the approval date of the promotion board report that non-selected the officer for the second time.” AR 135-175, paragraph 4-3(a)(5)(d).

Only caveat is that this provision only allows you to do 20 years, period. If any of those aren’t good years for retirement purposes it won’t allow you to stay in for that.

Having gone through this, check out other federal job options. My active duty as a captain terminated on a Sunday, and on Monday, I started my civil service job as a GS-12.
Retired from the reserves with 28 years.

How long do you have in and is there an up or out in USAR for majors? When I commissioned major was indefinite and only the last few years did that change for the active component. I would check first for a hard up or out for majors in USAR.

I was facing this scenario. I had 16.5 years AFS and wanted to get an active duty retirement. Was in the Reserve as a TPU and removed from scrolls on my first look at 05. Decided to resign my commission and enlist on active duty. Grade determination made me an SSG; I’ve been doing it the last two years and am now 18 months from retiring on active duty…with O4 pension…and at the rank of MAJ. No one seemed to know how to execute this transition, was lucky a recruiter at my local recruiting office knew. Turns out, you have to initiate the process through your local recruiting office. It’s very much like a normal enlistment, but you submit paperwork to conditionally resign your commission once your enlistment is official.

One of the Drill Sergeants at Ft Benning in 1977 had been a CPT in VN, but was RIFF'd in the mid '70s.
He retained his USAR commission while on AD.

Later in my career in the Guard I had a couple of former commands who were not able to complete all the education requirements and they too reverted to NCO ranks. However when they retired they did so at the higher rank.

You need to get enrolled in ILE and complete it. It's not hard. In fact I put it off for years, and had decided to retire as a Major. I read in your comments you are at 15, so you have awhile before 20. Once I enrolled in ILE, I really pushed myself through the distance program and completed it quickly. From the day I enrolled and started (1 April 2020) until I got my last assignment back graded (July 2, 2020) was only three months. I did that by working on it a few hours a day in the evenings and weekends, plus plenty of days off waiting for the next module to begin or waiting on grades. You don't have to do it that quickly, but you can finish it before next year's board. You have two Ps, but you can get a third look and be selected. Once you are selected, your MRD is automatically pushed back to 28 years.

I was a two time non-select for MAJ. I was sent a letter for SELCON which (Selective Continuation) gave me the option to continue to serve at my rank until I reached 20 years of service (this gets extended if you get promoted before you reach 20 years). At the time I only had about 12 good years and I decided to take the offer to be eligible for retirement. I ended up making the promotion list the following year (2020) on my third look.

SELCON is based on the needs of the Army so I'm not sure if that is an option currently but it may be worth looking into.

Not an expert on the Officer management, however, I had a friend (active duty Major) who accepted a RIF to the grade of SFC from Major as his branch was tight and he did not wish to vice up all of his years in service at his then age.

Not sure if that is a thing for USAR.

Would this be your first "Passover?" If so, you might still have a shot, if you complete your ILE prior to that promotion board meeting. Also, what is the grade authorization for the slot you are in? I would seek one that is authorized Lt Col (O5).

Is there a chance for you to be SELCON? I had a CPT who was SELCON every year because he didn’t have CCC (tried a few times, couldn’t pass or just didn’t complete), but he was allowed to stay in as a CPT. Not sure if the same is true for Field Grades, but worth looking into.