-Not necessary.
2. 人事處人員對於辦延期H1-B不是很熟悉. 如果延期H1-B需補充材料, 或被拒,而我在1月2日後返回美國, 會有問題嗎?
-No.
3. 如果延期H1-B發生問題,我會有身份嗎?我必須申請EAD卡以防止意外嗎?
-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.