-Not necessary.
2. 人事处人员对于办延期H1-B不是很熟悉. 如果延期H1-B需补充材料, 或被拒,而我在1月2日后返回美国, 会有问题吗?
-No.
3. 如果延期H1-B发生问题,我会有身份吗?我必须申请EAD卡以防止意外吗?
-Usually, USCIS will not deny the extension. So, you do not need to worry that much, and do not need to do anything.
But for your question, my answer is:
you do not have status problem even if the extension is denied (your status will be AOS in that case). You need EAD to work if the h1 extension is denied.