When the winner offline over 1 week not mark reveived. Could I request new winner?

yes you can.

As short answer as your description, but the answer would be... Yes.
For further questions in general recommend taking a look in the FAQ :}

Has he been online on steam and have you tried contacting him there? You should try that first, after that you can request a reroll.

why you don't wait for 'em to get online first but yeah you can

Yes you can.

Just make a support ticket=> Request New Winner => other => More than 7 days and not marked received.

don't close and open new tickets, they get pushed to the end of the queue.

I am in the same situation at the moment - first time I might have to request a new winner as the winner hasn't activated and marked it.
But I am wondering: My winner has been online here on SG during the last week (multiple times) and on steam. I have sent him an email asking to activate and mark the key as received. He hasn't. But he might well have passed the key on to someone else. So if I request a new winner - it might be possible that it won't work, right?

So how are your experiences? Does that happen? Or can I be more or less sure that a new winner will get a working key?