How Is Bass Divided Among Speakers If No Sub?

Yes, your processor controls bass distribution. If you have all your speakers set to large, all get full range sound. If you have any of the centre or rears set to small, their low frequencies are sent to the mains. If you do not have bass processing on your amp/receiver, then all speakers work full range.

Obviously, only the channel(s) getting the bass will produce it if all speakers are set to large. Although bass is generally non-directional, so regardless of which speaker it comes from it will likely sound as if it's coming from everywhere.

The downside to setting all speakers to large is that bass frequencies really suck a lot of amp power, so typically the mid-band will suffer. That's why most people use a sub, it lessens the load on the amp. I expect also that most low bass sound effects are mixed to the main speakers anyway, so running centre and rears on large doesn't make a lot of sense. Very few centre/rear speakers can handle deep bass.