I plan on being in Croatia in late October. The RS book says that the islands sorta shut down and people head inland during off season. I wanted to check out an island (or two) but am afraid it will all be closed down. I am fairly certain it will be too cold to lay on a beach (highs in 50's-60's on average). So am I better off staying inland like Split? If not, I would like to visit Hvar.
We were in Korcula (near Hvar) in October a few years ago--it was very quiet and some of the restaurants were closed for the season. Also, the ferry runs less frequently off-season so you need to plan your travel for days that you're sure the ferry is running. We still had a nice time there and for us, it was worthwhile going--even off-season. Another town near Split that we liked was Trogir. We stayed in Hotel Vila Sikka.
Which island are you thinking of? You mentioned Hvar, which is absolutely fantastic. Ever since my first trip there a few years ago, I can't imagine a summer without it, or at least Croatia. I can recommend a couple of different private accommodations in Hvar if you decide to go there. The lady that we usually stay with there says she has guests ALL months of the year, and that there are some people who go swimming as late as november. You shouldn't have a problem using the ferries in october.