Maintenance for the week of April 22:
• [IN PROGRESS] Xbox: NA and EU megaservers for patch maintenance – April 24, 6:00AM EDT (10:00 UTC) - 12:00PM EDT (16:00 UTC)
• [IN PROGRESS] PlayStation®: NA and EU megaservers for patch maintenance – April 24, 6:00AM EDT (10:00 UTC) - 12:00PM EDT (16:00 UTC)
There are only few items that you could consider "permanent". The deciding factor will be demand. If people continue to buy them, they stay. Once every who wants them already has them, they go.
The ones with a short store life tend to be the "special offer" ones that need the slight demand boosted by exclusivity.