i don't think kakashi loses an eye in battle. i think the surgery removes his eye and implants the sharingan (more than likely obito's) eye in him.

and i'm going to venture a guess and say it's a large scale battle/mission in which obito gets killed. it seems cliche for obito to "save" kakashi, not to mention the sheer difference in power right now, it doesn't seem likely except in extreme corniness. maybe more like obito/rin/others getting ambushed in a big fight that could've been prevented had kakashi not been as arrogant.

not to mention, i don't really feel like there's much of a bond between kakashi and obito right now. kakashi talks about him pretty fondly in the future, and right now just having obito be a doofus-turned-sacrificial-hero doesn't cut it for me. there's got to be something more to it...