Other than the obvious gross factor, it's possible that the drinks cooler is the same temp as the morgue drawer. ie the body might have (in 5 days' time) ended up the same either way.
But given that 2-4 people die each week on a cruise ship somewhere (1 out of 150,000 passengers), you'd think that "how many days can a body be kept in the morgue drawer" is a known number by at one or more crew members on every ship. Which implies if death occurs early in a 7-night cruise, the body and relevant passengers need to get off at the next port to get home. If it occurs late in the cruise, then you have the option of staying on board until normal disembarkation.
Or something like that.