In response to two recent questions:
Miles per day. I took one rest day (where I still tooled around a little bit). On the other 20 days, I rode at least 100 miles per day, and on at least 4 days I got over 350 miles in a day. I think that 400-450 miles in a day would be pretty close to my absolute limit. Even the 350+ days were pushing it, in my opinion. My hat's off to the Iron Butt folks.
Return trip. I ended up storing my bike in Anchorage for the winter. I plan on returning at some point next summer and riding the bike back down, though I'm likely to take a different route (Cassiar Highway instead of the Alcan) and may well take a ferry for some portion of the journey.
I did explore the possibility of selling the Rebel in Alaska and just buying another one (or a 500) back in the lower 48. I was laughed out of the Honda dealership when I proposed trading it in for credit at another dealership, and I only received demoralizing scam responses when I listed the bike on Craigslist. It appeared to be virtually impossible to sell a bike in Anchorage -- even at a substantial loss -- right before winter.