I'm going to have to lean on whether or not there is terrain/buildings to deal with.
In an open field I think the Orks would eventually overrun the Terminators, albeit with with ridiculous casualties.
If there is terrain or buildings to deal with, a couple of Terminators could easily setup choke points and kill the Ork forces trying to push though.
But we are all forgetting the real problem here! I don't think my kitchen table is big enough to hold that many models! (joking)