Yes, I think it's possible if you have access to the internet and use it well. I have several students at C1 level who have never spent more than a few weeks at a time in an English-speaking country. They all spend quite a bit of time watching English movies, taking online lessons and reading in English. I think the key thing is spending time doing something in English every day, even if it's only for 20 minutes. Good luck!

Yes, it is certainly possible. Aisling is right: the Internet makes it much easier.