回複：如果員工換工作後，公司是不是必須要通知移民局終止這個已走員工的Ｈ１Ｂ呢？謝謝

If you don't inform USCIS, you may be liable for future H-1B wages and return travel expenses. As an employer, you may try to minimize your legal exposure. However, in practice, employer may also inform the employee of its intent to file a termination notice to USCIS as a courtesy.