Sitting on the center of the Satellite crash site for the Code and base is killed

The crash site red area is a visual marker. Nothing special will happen if you're killed (either by an enemy or the forgotten) during that 3 day countdown. On many worlds you don't sit in the crash site itself but next to it.

If you killed on the crash site, move out a short distance, then if possible move a new base but beware of cooldown periods. Try to have a base ready to move once the satellite crashes.

Got it. So for short, while it is within the time period, you can always change base incase the first one was destroyed. Thank you.

You must to have the base during those three days in the proper place where the satellite crashed. If your base is destroyed that time frame is reset. When you put another base, it will start over from scratch and you will have to wait three more days until you get the code.
It is advisable to provide some security to the base that you put to obtain the code, either with the support of other bases of yours or with other bases of alliance partners.