what happens, if I choose to ignore disbanded

Your opponent would ignore all team abilities, you would not. Not sure the finer subtleties of this, but that's how I'd interpret it

Not quite

It would mean your team abilities work, his does not

Major dif for something like Mystics and CSA

Q: Does Disbanded! cancel/counter the Assembled Battlefield Condition?
A: No. Disbanded! renders team abilities null and void and Assembled works off of team symbols.

Based on the above, from the FAQ/Errata, the person who ignores disbanded does not lose their team abilities.

But say you've got E Ragman, and he's got V Blue Devil (both Mystics). If Ragman hit's BD, wouldn't Ragman still take the Feedback? And if BD hit's Ragman, wouldn't he ignore said feedback? The card says ignore ALL team abilities. If you ignore the card, then all team abilities are still in play for you, but not for your opponent. I may be totally off on this though, but *shrug* they left this one out when they summed up the effects of theme teams on BFC's (probably because it was retired when theme teams came out)

If I bark a command at you to 'jump', you fill in the 'you' part

I understand the card to mean 'you (meaning both players) do not get to use your team abilities in this game'

If I ignore it, and you don't, then the card now means 'you (as in person being addressed) do not get to use team abilities in this game' not 'you ignore your own team abilities and his'

Ignoring a BFC is supposed to be a positive.

The RA may rule otherwise eventually (fat chance he will rule anything on this, just like keywords for retired sets) but this is the way I will always interpret it

And I agree with BigSoph here.
If you ignored Disbanded, you would be able to apply your TAs, while your opponent would not be able to apply theirs, whatever the application.

Based on the (long) laundry list of how the other BFCs work under the keyword "ignore" clause, I'd say that Kersimus is correct. It may seem counter-intuitive, but take a look at how they ruled Armor Wars, or any of the other "beneficial" BFCs. (They might also go the route of "There are no TAs on your opponents actions, but there are TAs on your actions." That would be similar, but I think subtly different from what we were talking about.)

If the card actually said that, you would certainly be correct. But ignoring all team abilities has both positives and negatives to it, and if you keyword 'ignore' it, you ignore the ignoring of all TAs.

Of course, there is no official ruling, right? They hadn't addressed the "retired" BFCs last I checked...