Never been there that late, I would think that the slough will not be accessible at that level, which would mean some logistics in getting your gear back to the takeout. There are folks who will shuttle your gear via atv back to the takeout--not sure how you would nail that down in advance though. The 'doors' will only be open into the lake--no cheat route--so the icebergs blocking the entrance could come into play. Make sure you scout that well.
An excellent guide is published by Russ Lyman at Cloudburst Productions--do a google search. He will have pretty much everything you need to know on this trip, great guy and very helpful if you decide you need to call him in person.
Pm if you have any questions, I've only ran it 3 times, but I'll give you whatever advice I know. One of the best trips river trips on the planet in my opinion.