Cant comment on the Orchestra but on other MSC ships there is always a Midnight buffet that has a different theme each night and a grand Buffet on the last evening. Also waiters usually wander through the public areas with pastries and sandwiches later on.
Last MSC we travelled on only can around at 1130 to 1145 with sandwiches or a spread in one of the lounges.
on this cruise did have one galley buffet which was excellent
unless they have changed there are only set meal times no 24hr food or alternative evening meals unless you use the pizzeria (paying) 7-10 on these ships.
Drinks were beer 50cl 5.40 euros coke 2.50 euros cocktails 6.40 euros