Senior practitioners & instructors. Would this be unethical towards our instructor or am I just overreacting?

Many good answers so far.

Life gives you lemons; make lemonade.

In my experience a ship can only have one Master. You may have to open your own school, or stay where you are and serve only one master at a time.

Accreditation is not all that it is cracked up to be. Some folks think it is the thing that makes martial arts. Life has shown me it is like anything else. The proff is in the pudding.

Don't fret over it. Just commit to do one or the other. If you stay accept what it is. If you go leave on good terms and with respect. Don't worry about the rocky boat. If it stays afloat or sinks it won't be because you stayed or left. It will be because the Master put it on the rocks.

I can understand your worry, but I agree with the idea that you are overreacting. Your head instructor is gone, and quite possibly will be gone for good. Having made that clear before he left, I'm sure that he would understand that you all need to do what you need to do to continue with your own martial art studies.

Before I comment more, the BJJ certification is what the assistant is going for, correct? How is this a style conflict with the Shotokan instructor?

EDIT -

I don't believe that this would really be along the lines of a corporate takeover, as I know of and have trained at several schools with two or more senior instructors, who also teach different arts. There may need to be a coordinating of schedules, but it really shouldn't pose too much of a problem.

Something that I have learned in the past that I think would translate well to your situation is waiting for what you want to happen. I understand your reservations and desire to resume training with the Shotokan Sensei when/if he decides to return to teaching, but that could pose detriment to yourself, the others, and the school as a whole.

There's an old Buddhist saying that goes something like: Wanting and having expectations will not make you happy, and will more often end in failure. Reacting to what is, in a way that moves you forward will end your suffering. Basically, while you enjoy martial arts and that is your lifestyle, the desire that is driven by your loyalty to your Shotokan Sensei, is causing you a problem, and may do more than just give you a headache. Instead, you should look to your future, see this moment as something you should work through, and step up to continue your training with the assistant instructor, and possibly a new one. (It may not be what you "want", but it is what "is".) Who knows, maybe the Shotokan Sensei will be happier with this move, and it may help to ease his own stress.

From where I stand i don't see how it's possible to continue Shotokan training until your head master returns, at least at this current state. My personal first instinct would be to find a high ranking shotokan practitioner that is actually accredited to teach.

My personal thoughts on the whole BJJ accreditation is that you should divide the school into separate classes while the instructor is away. Instead of having one school for shotokan, you can have multiple schools teaching at the same building. A rotating schedule that would train alternate arts on alternate days. Once your shotokan master returns, you can return to business as usual. Of course my view is influenced by my old Hapkido dojang, where they would have many arts training in the same building in different time slots. We had Hapkido, some karate style (I'm not sure which), jujitsu, aikido, and judo all going on at the same place.

I'm going to say you are overreacting. The circumstances you are facing is not the nor. However, it is what it is. You can't control what is happening. You much like your martial arts training must learn to roll with the punches. In you aikido training you just have to blend with your situation. You have to adapt to your environment. In life we all have circumstances that come up that we haven't planned. You have to adjust and keep moving in the midst of your challenges. Apply this to your martial arts development.

I'm not sure if you realized that you changed the spelling from jujitsu to jujitsu. There is a difference. Also, what you describe that you are training is is actually jiu jitsu (BJJ). Again there are differences.

That is a predicament, but not one that has never happened before. My teacher had once told me of a dojo mutiny after his initial Karate teacher refused to progress and propagate the style that they were practicing at the time.

The fact is that you need a leader and someone who can appear authoritative during your teacher's absence.

This assistant instructor seems to be capable enough to handle the task set before him, if he can not progress under your teacher, he must receive validation from somewhere or else your group is going to permanently fracture and dissolve.

When there is a void of teaching, students will either rise to the occasion of cease practice all together. Many famous Karate masters, having lost a teacher for this or that reason, would seek out another.

Personally, if I were the head teacher, the propagation of the art comes first and foremost. It will endure long after my death, provided I sow the seeds with the entirety of my heart. Even if I had to teach in a slum.

But, ideological difference aside, you need someone who appears in control. Not just being in control, but someone whom has the proper credentials to be in control.

I second Flawed_logic's suggestion.

Creating a new school might be able to help you avoid the friction from switching "allegiances." It might entail extra administrative work, but it would make things a lot easier when your shotokan instructor returns.

I think you should contact the organization and see what they say.