20>10>5> You know where it's heading.
It's heading towards the right direction and it is only possible by the capable manager. Now there will be very few or zero post bursting in this campiagn. That's an ideal limit and should be for all the campaigns.
Even if they limit further it will be idle as all the thread you go you see someone with the signature and with the huge number of participants they get what they are looking for i guess. The ideal limit depends on the budget of the campaign and if they have any issue they can limit the number of participants.
I believe yahoo might give notice well in advance for when the campaign would come to an end.
If they stop the campaign i doubt yahoo might know that before hand as he said that his only mode of communication is through this forum.