Rathlin Gaelic was quite similar to the Gaelic of Islay which survives to the present day.
Indeed, if I was to set about reviving Rathlin Irish, I would learn the Irish of Tory and the Gaelic of Islay in order to strengthen what can be learned from books and tapes.
You can learn a bit of Islay Gaelic daily by following Ionad Chaluim Chille on Twitter!
Dé Céadaoin, Eanáir 09, 2013
Young, Rose M. (I); MacErlean, J.C. (II): "Irish in Rathlin I-II and notes", Irisleabhar na Gaedhilge 6: () 139–41Laoide, Seosamh: "Irish in Rathlin III", Irisleabhar na Gaedhilge 6:* () 139–41 (notes on Irisleabhar na Gaedhilge 6 106–10, comparison of Antrim Glens with Oirghialla)