What happens if the atf bans braces?  What happens to the weapons status?

They are classified as pistols.

I think you are wrong. Because ar and ak pistols can not have vertical fore grips?  It changes the status to an a o w?  

But, the firearms being sold here have the overall length of 26 inches?  Which precludes them from a o w status?  

Does on just take the brace off?  If it comes to that?

The brace has no bearing on its status as an "other firearm" because ATF already ruled that they do not count towards OAL. So removing the brace wouldn't change its classification.

The brace doesn't count, but the receiver extension does, if an AR, no?

That's correct, they even explicitly say so in this letter regarding braces and OAL measurement: https://princelaw.files.wordpress.com/2019/07/atf-folded-brace_redacted.pdf
(first paragraph on page 2)

So, the brace stays under the proposed new rules?

The new proposed regulations are alarmingly vague and go beyond even just braces. If you read the proposed regulations they're now going to be taking in to account other factors too including size, weight, caliber and optics. ATF is seemingly moving to a very scary subjective standard of "we'll know a SBR when we see one". This is bad news for everyone, especially NJ where registering them as a SBR is obviously not even an option. It's too early to say for sure right now but most likely "other firearms" probably won't be impacted as badly as AR pistols because they're already not "designed to be fired with one hand". Worst case scenario is that you'll just have to remove the brace to keep them legal.

I appreciate the info.

I called modmat today they said the weapon I purchased was approved by atf.  I do have a copy of the letter.  But what I'm trying to figure out is the brace itself the part that needs to be registered?  

Or the weapon that has the brace or any combo of weapon with a brace?  It is as clearly as mud mostly likely by design.  
Any clarity to the about questions would be great.

If you bought a factory firearm with a brace that has a letter specifically approving it you *should* be ok. The new regulations essentially boil down to "if ATF hasn't approved the exact configuration of your brace equipped firearm it may or may not be legal"