I just gave my notice at work today. Im leaving Taiwan for good and told them id stay till they found someone. Also currently reporting the pricks to the labor bureau for various reasons that I will update here eventually. Once my ARC is cancelled by them I assume they tell the government to cancel my work permit, then guess ill get a call from immigration to get out of the Wan. Assuming They cancel it Monday, how long will the process take? How long will immigration give me once i get a call? Id guess the whole process would take 2-3 weeks?
Employers can’t cancel ARCs. They sponsored you for a work-permit, so that’s all they are able to cancel. Once the BEVT gets notification that you are no longer employed at your sponsoring company, they will cancel your work-permit and then they will inform the NIA that you no longer have a work-permit and the NIA will cancel your ARC because you’ll no longer have a valid reason to reside in Taiwan.
How long do you have? Depends on when your employer calls the BEVT. Depends on when the BEVT cancels your work-permit. Depends on when the BEVT notifies the NIA. Perhaps 2 weeks, but you need to know when your employer calls the BEVT to cancel the work-permit. If they will hold off canceling your work-permit until they can find a replacement for you that would give you the most time to either find a new company to sponsor you for a work-permit, or get your affairs in order and GTFO! 
Thanks, actually i got a plane ticket already, just wondering if ill have to leave before Dec 19, no plans to look for new work.
You will probably be just fine until Dec. 19th. If you want to be sure, just go down to immigration and tell them you want to cancel your ARC. They will almost certainly extend your passport to that day. Believe it or not, when it comes to ending ARCs and leaving Taiwan, they will gladly give you up to a month if you need it. They might even give you more if you have a good reason.
Bring your ARC, Passport and plane ticket with you, and ‘give yourself’ an exit date, otherwise you’re just hoping BEVT and NIA work slow.