If a vote is held today, or later this week, to decide whether to admit Palestine as a participating state in the negotiations for an Arms Trade Treaty, this may determine whether the Diplomatic Conference will even effectively start. An historic decision to admit Palestine would most likely lead to Israel and the USA (and possibly others) walking away from the conference. It would, however, be a terrible mistake to allow the negotiations to collapse.
It is argued by some that the pressure to admit Palestine is a machination by certain states opposed to the idea of an Arms Trade Treaty. If that is true, allowing the negotiations to collapse would be yielding to those states. Thus, the remaining participating states should continue the negotiations and adopt as strong and effective an ATT as possible. In any event, Israel and the USA would likely not ratify an ATT (though for different reasons), so why should their absence torpedo the talks?
Palestinian statehood and an effective Arms Trade Treaty are not mutually exclusive.