answer to question number one: the chance is unlikely you will save the change at the exact same time so both changes should be in the history which you can view
Yes. That does happen, however that requires that one or the other realize that overwrites are happening and then someone has to manually merge the two.
I'd love to see wiki style sections so that people can edit just a part at a time, but it seems to me like locking would be quicker to implement right now.