Giveaway winner revealed key but didn't activate it after 7 days. What do I do?

I'll do that, but if/when they ignore the email what do I do then?

It's a level 5 user

I would rather not reroll if I can avoid it. The key has been revealed now so I can't guarantee the next winner will get a working key. And I want to keep my perfect giveaway record. I will do that if I can't find a better solution.

Good call, worst that happens is they deny my request. I sent the ticket and will report the outcome

That's easy wait for 7 days after the giveaway has ended then mark the game as not received or (optional) you could write in the giveaway comments that you're ok with deleting the giveaway.

It seems to be your first win, so let me tell you, pushing the GA creator for the key is not considered good manners. I understand the impatience on your first win, but as per rules the GA creator has 7 days to deliver the key. After these 7 days have passed, it is appropriate to try and contect them, but before it's just rude.
When people would do that with my giveaways, I would just make them wait the whole 7 days.

To add on to the above replies:

In short, there is a common courtesy waiting period for both giveaway creators and winners: one week for the creator to deliver the key, and one week for winners to activate the key. After which, attempts at communication should be used to try to resolve any issues before resorting to contacting Support.

I suggest you read both the "FAQ" and "Guidelines" pages linked at the top of the website under "Help" for more information.

And welcome to SteamGifts.