I would imagine that they would still have some sort of holiday to honor and remember their fallen heroes. The Dominion War alone killed thousands--if not tens of thousands--of Starfleet personnel.
We know from Starship Down in Deep Space Nine that they still have hot dogs in the 24th century. But I can't help but wonder what would the hot dogs be made of in that era. A tasty meat substitute?
We also know from The Cage that they still have picnics in the 23th century.
We also know, from the last Voyager episode, that they have fireworks, as well. So, whatever memorial holiday they celebrate to honor their fallen heroes, it can't be too different from the way we do it now.
Just throwing my two cents out there.
Sean