The Jerusalem Talmud did not cease to be studied through out the ages. In Babylonia, the authors of early Halakhic works (originating from Sura) such as Halakhoth Gedoloth, Halakhoth Pesuqoth and Halakhoth Ketzuvoth follow some rulings of Eretz Yisrael over the Babylonian Talmud. This could be due to the Palestinian origins of the Academy of Sura founded by Rav who descended from there. Actual incorporation of the Jerusalem Talmud is attested in early Geonic works such as Sefer Ha-Hefez and Sefer ha-Methivoth which cite the Babylonian Talmud and the Jerusalem Talmud in tandem.
Numerous Medieval Authorities continue to cite it and interpret it in their novellea and compositions on the Babylonian Talmud, notably Rabenu Hananel, Ramban, Ba’al ha-‘ittur, Rashba, Meiri and even the Tosafoth. Maimonides gave great weight to the Jerusalem Talmud and was criticized for ruling at times in favor of it over the Babylonian Talmud. Maimonides even composed a compendium of its laws similar to the Halakhoth Gedoloth of Rabbi Yitzhaq al-Fasi on the Babylonian Talmud.
The Jerusalem Talmud continued to be studied and cited by Acharonim. R. Yosef Karo, as an example refers to the Jerusalem Talmud thousands of times. Complete commentaries on the Jerusalem Talmud, (rather than simply interpretations of selections) surfaced already as early the Expulsion from Spain and today are numerous. (see https://sites.google.com/site/jtalacad/bibliography – for a list of scientific and semi-scientific commentaries).