That's the best failure mode you can expect for the average user without diving into the usability pit that is git - both changes are kept and it's obvious to u

That's the best failure mode you can expect for the average user without diving into the usability pit that is git - both changes are kept and it's obvious to users that there is a merge conflict. Otherwise, one update would just eat the other silently, leaving one side confused and the other oblivious.