FOOL: That sir which serves and seeks for gain,
And follows but for form,
Will pack when it begins to rain
And leave thee in the storm.
But I will tarry; the Fool will stay,
And let the wise man fly.
The knave turns fool that runs away;
The Fool, no knave, perdy.

William Shakespeare (1564-1616) English dramatist and poet

King Lear, Act 2, sc. 4, l. 84ff (2.4.84-91) (1606)
    (Source)

Perdie, perdy: "by God" (from the French par Dieu].