Help! I just erased an important contact

I assume when you say "erased" you mean permanently deleted, not temporarily omitted or filtered. If deleted it is best to restore from a backup asap (before entering more data).

Note: First check to make sure that a temporary filter has not be applied to the contact name column. New users often think that they have deleted records, when they have only been temporarily omitted by a filter. When a filter has been applied to a column, a filter icon will appear on the column header.

Like this, you can restore your data. I hope this helps!