The Work Permit is a piece of paper, a letter. You should have a copy. The employer should have a copy. The government departments involved will have one copy or multiple copies. The Ministry of Foreign Affairs will probably have a copy. Vice President Lu may get a copy, etc.
It will be clearly stated on the Work Permit as to the beginning and ending (i.e. expiry) dates.
It does not matter who holds it. It matters whether the employer notifies the relevant government department and Police Station that your employment has been terminated.
If your employer tells you to go take a hike, but says that he will not notify these departments that your Work Permit has been cancelled, i.e. he will just let it run its course, but then not renew it, then (assuming you have some savings) you can go to south Taiwan, sit on the beach, and watch the boats go by.
You can also try to find a new job, and then try to arrange for the new hiring date to occur roughly a week or five days before the expiry date of your old Work Permit.
Granted, it is not fair that the employer wants to unilaterally cancel your Work Permit. However, from a practical standpoint, even if you want to file a complaint, and/or sue, you need to be on a firm “residency” basis before doing so, and that requires the negotiation of a new Work Permit (in order to get residency rights based on employment), or marriage to a local citizen (with accompanying application for the appropriate marriage visa, commonly called JFRV), or a decision to devote your life to Buddhist studies (thereby obtaining a religious visa), or some other related purpose of residency, in order to continue your soujourn in Taiwan.