It is rare that the moderators will "delete" a whole thread. Usually, a thread is "deleted" only if it is found be in direct conflict with the User Agreement. The moderators will, however, lock threads and remove them after notification in certain situations. The User agreement can be found here
and some general guidelines for how we moderate and suggestions for posting may be found here
However, there is only so much space and unfortunately, we have to remove some older threads to make room for new ones. In order to have this done in a more consistent and fair way, some of the busier forums are set up on “auto prune” so that if there is no activity on a thread for a certain period of time (ie: 30, 60, 90 days etc.), the Message Board will automatically delete the thread from the board. My guess is that was the case in this particular situation. Chances are, the thread had not had a response in the designated time period for that forum and the Board automatically removed it on its weekly sweep.
So if it is a topic that you would like to continue, I would say perhaps you should start a new thread and see what responses you receive from our ever evolving membership.
I hope that helps.