Don't worry too much.

1。我的绿卡3个月前才被批准。因销售业绩下滑将被裁员，明天是最后一天，公司会有一点补偿，请问这种情况被裁会不会影响我的绿卡。

不会

2。我有3周年假没有休。公司是否应该补偿？

Will pay you for the three weeks.

3。请问如何处理401K?

You can leave it there, or transfer to company like Vanguard, fidelity etc.

4。请问如何延续医疗保险？

You HR dept. will tell you in detail what you should do.

5。我会尽快找工作。但不知前景如何。我积蓄不多，我是否有资格申请失业保险？如何申请？

有资格申请失. But I would not do it unless I absolutely have to. You HR should know how to apply for it.