Without Gaudreau this team is awful. You either sign Gaudreau or go full rebuild. You could maybe try to cram in another superstar UFA. Not sure who that would be though. The next best UFA is Forsberg, who is probably almost as expensive and not as good.
There's nothing to indicate that Gaudreau, who is a late bloomer, won't be fantastic for the next 4+ years. With any big signing the last couple of years are likely to look like overpayment six years down the road.
The priorities, in terms of re-signing the big guns, should be Gaudreau, Tkachuk, and then Mangiapane.