I don't think the shutdown will effect Buzz much if at all. Buzz is one of those rides that tend to handle large amounts of riders. We were there in December (1-7) and did it standby once. It was a little frustrating because they give out so many FP+'s that standby even when it seems short goes pretty slow. A new CM was working the merge point and people in front of us starting getting frustrated because she was very precise in her counts. 100 FP+ riders followed by 10 standby. We knew because the people in front of us were counting and announcing the totals. At one point she had held both lines to answer the phone and the people in standby just starting going in since her back was turned. When she saw it happening she went wild yelling at people to stop and come back, etc. She was moved from that position pretty quickly after that.
So the moral of the story I guess is a FP+ to Buzz is seemingly always available during the day once you use your first three. Don't worry about the wait, just do a same day FP and you will be fine. We have ridden multiple times in the same day doing it.