Dubrovnik and Split in late Oct.

Definitely cooler with greater prospect of rain. The coastal villages vendors (rstaurants, retailers and bars) are predominently closing due to the small ship cruises, from whom a great number of tourist arrive, end their season by mid October. Water temp definitely too cold to swim.
However, what are you seeking to gain during a visit to Croatia?
Wonderful people, peaceful walking experiences, excellent prices and several alternative transportation modes (ferry, car) still offer the chance to create a memorable journey.

Based on my research when planning our trip for last September, I wouldn't go to the islands in late October. However, I would think that restaurants, hotels, etc. would still be open in places like Dubrovnik, Split, and Zagreb. You could certainly look up hotels & restaurants for these places to see if they are open in late October. Zagreb certainly is not going to shut down since it's the capital of Croatia. The advantage is that there will be fewer tourists, and prices will be lower, in all of these places.

The coastal villages don’t get small cruise ships, but most close at the end of September, as it’s a short tourist season in Dalmatia, due to the weather. The larger places such as Split and Dubrovnik are home to many people and are therefore open year round and there is enough here to keep you occupied for a few days.

The Croatian ferries and catamarans move onto their winter schedules around 6 October, which indicates the end of the tourist season.

You are brave risking Greece in November - that can be cold, wet and miserable too!

Thanks for the feedback. Unfortunately we are locked into the timeframe as we have an event in Greece the first weekend in November. Looking at adding a few days in Santorini to the list with the hope that it will be warmer and sunnier and that we will miss a lot of the tourist there.

I was in Split and Dubrovnik for a day each as stops on a cruise in October 2011 and it was a good time to be there. It was raining like crazy all day the day we visited Kotor but we had good weather in Split and Dubrovnik. It was more mid-October but Googling Dubrovnik climate I don’t think the averages look daunting. I don’t thing you have to worry about these cities totally shutting down, they are not just tourist stops. Some places may be closed but there will be fewer visitors too. Check on the transportation connnections though, last time I checked Greece and Croatia were not a natural combination despite proximity. I.e. you might think it makes sense to combine these but the logistics might make Greece and France just as practical. Just like Spain and Portugal seem to make sense on one trip, but the logistics are not that great.

I was in Split and Dubrovnik in late October a few years ago. Both cities were bustling, with plenty of tourists. Weather was great. In between I stopped in Korcula, which is kind of like a much smaller Dubrovnik. The 'end of the season' was much more evident there-- very quiet with a lot of the restaurants closed. Overall was a great trip.