Assuming you can't source a replacement, maybe the outer thread of the Timesert is one that you might find on a nut at the hardware store (or close). If so, buy two such nuts and cut them down so you can get two on the Timesert, forcing them together in the double-nut locking technique. With the plug in the vise and a wrench on the double nut, the Timesert should give up. I wouldn't try to say whether or not a Loctite approach would work, but it makes me itchy thinking about it. Now, Using Loctite when replacing the insert might be the right thing, but you need to know if the breakdown temperature is greater than head temperature.
Richard L.