Greetings,
Not sure if you are asking for putting a CASE inside a stored procedure or if you want a single SELECT to use the CASE statement. It sounds like you already have 3 different SELECT statements to return your values and just want to have a flag turned on if any of them return a result. If so, then maybe this will help you.
DECLARE @CheckFlag tinyint
SET @CheckFlag = 0
IF EXISTS(SELECT * FROM MyTable WHERE Checks1 = true)
BEGIN
SET @ChecksFlag = 1
END
IF EXISTS(SELECT * FROM MyTable WHERE Checks2 = true)
BEGIN
SET @ChecksFlag = 1
END
IF EXISTS(SELECT * FROM MyTable WHERE Checks3 = true)
BEGIN
SET @ChecksFlag = 1
END
RETURN(@ChecksFlag) -- OR Just use it from the procedure.