BF1942 had a simple text edit that could take you to 128 on both teams just fine... Nobody played it that way back then because of the network bandwidth requirements. (even the best internet couldn't keep up) Bots always sucked on those too, due to CPU requirements, and the limit of single-threaded computation.
To OP, you're unlikely to find any truly offline massive games. The closest you'll get will be bots in certain multiplayer game modes of certain games. (like the Battlefield series) If you're willing to go online though, you can give Planetside 2 a try.