Any idea when he goes before Issa's committee?
I can't speak to the other committee or it's schedule. Issa does make the point that his own committee had been stonewalled and so, this may be his only chance to ask these questions at all. There is a chance that Holder will never have to go to that committee for a hearing and it is fairly clear at this point that Issa's committee has been 'played' by the DOJ and the White House.
So, I do not expect Holder to go to another Issa hearing and even if he does, we will only get more of the same. The only way that Holder goes back on the stand under any duress is if some whistle blower leaks something really damning to the DOJ; which is quite possible. It is an election year, and so we can expect a steady drip of leaks on various scandals to be released, including Gunwalker, up to and including election day IMHO.