I'm not panicking at all.
Miami is the best team in the league, and their core and play style didn't change in the offseason. Meanwhile, we have only 7 returning players (one of which, Bradley, is injured, and two more, Green and Wilcox, coming off major injuries). There is an adjustment period, and we saw some of that last night.
Rondo will continue to be Rondo. Pierce will continue to be Pierce. KG will continue to be KG. JET, Green, Sully, and CLee will all adjust in time, and when they do, we will be a team that opponents are scared to play.
I'm not worried. The things to remember here are to have patience and trust Doc.