Jami, what a ride! Sounds like you had a great experience, bike problems and all.

For what it's worth: I had sudden and unexplained oil usage in my old 1996 Tenere 660 at about the 30,000km mark. It was Motul 300V 15W50, and after about 1600km into a journey the bike suddenly started using oil very rapidly. Luckily I did check the level in time, but it was well below the dipstick, like yours. I just poured in some el cheapo semi-synthetic (as there was no good stuff available) so I could keep going. After changing the oil back to another brand of 15W50 full synthetic, I had no further issues.

I realise it's an opinion offered too late, but I've discovered that taking oil levels for granted in dry-sump single-cylinder engines can be dangerous. Why do they use it? I don't know. I check mine every time I stop at the end of a day's travel. And 10W60 should be absolutely fine in a 660 motor imo. The manual allows 20W50, and there's not a great deal of difference. But in Australia Castrol Edge is a performance car/light diesel oil, and may be friction modified (don't know for sure), and thus may not be so good for bikes.

I hope any damage is minimal, and that you have safe travels in the future.