I had the e-Mail for my cape waiting for me in my inbox the moment I got home on Monday.
The e-Mail will go to the person that purchased the tickets. In other words the e-Mail address that is associated with the EventBright account that was used to purchase the tickets.
If you purchased your Minecon tickets some other way, such as from a scalper on eBay, then you are probably out of luck. The cape code will be sent to the person you purchased the tickets from, and they have probably offered them up for sale on eBay.