Sounds like you want to create a cleanup job that removes discounts. As long as you set the redemptions and expire date correctly, that should be a pretty easy job to write. 

Something along the lines with a job that:

1. Get all discounts in the system (get children on campaign root content, or if there is any better way)
2. Loop through them, check for the conditions you want, redemption limit/expiry date
3. Use IContentRepository to delete them

Hopefully that helps

Campaign or promotion are just normal CMS content, so here's what you can do:

• Get campaigns as children of SalesCampaignFolder.CampaignRoot
• For each campaign get promotions as children of it.

Now you have all promotions in the system. Checking the expired promotions should be easy enough. Checking the redeemed promotions can be tricky because there are three types of redemption (per promotion, per orderform, per customer) - but I guess you only care about the first one (per promotion). You can use PromotionInformationRepository.GetRedemptions to get back a list of PromotionRedemption for a list of promotions. For each PromotionRedemption, check for TotalRedemptions and compare it with the redemption setting of the promotion.

However I would say it's not necessary to delete the promotions that way. Promotion engine is smart enough to ignore the expired/redeemed promotions, and you can do the same with your marketing page. Keeping the promotions can be useful later when you look at analystic of how a promotion was used.