i understand the Alhambra will be closed when our ship is in port in Malaga on 3 October. Wondering if we should still visit Granada or if there is some where else we should consider.
Sure, there is still the cathedral and the royal tombs, good tapas bars, bit of Moorish influence in the goods and food as well.
Ronda is likely a popular daytrip offering as well, neat older town with a rather dramatic geography.
Malaga itself is also worth a day of wandering and eating.
I would stay in Malaga and explore there on a port day.
It would be a long bus ride to visit from Malaga. At least three hours each way. A best you would get a peak at the Alhambra. It needs a good half day if not a full day. There is plenty to see and do in Malaga for the day.
I'd stay in Malaga because of the distance to Granada and the limited time available on a cruise stop. Granada definitely has additional points of interest besides the Alhambra, but you wouldn't have a lot of time to see them by the time you chose a conservative time for your return train or bus to Malaga.