As Steve mentioned, once the data is saved or converted into varchar, there's no way to get the unicode data back.
If after the data type change, you still can't store the arabic characters correctly, you need to check your string handling. Here's an example of what I mean.

DECLARE @test-2 TABLE( MyString nvarchar(250));

INSERT INTO @test-2 VALUES('طالÙٱئذش'); --Random string without any knowledge on what it means
INSERT INTO @test-2 VALUES(N'طالÙٱئذش');

SELECT *
FROM @test-2;