You need to replace your images and host them on a proper site.
#.
ivory shuttle
Imgur is free? 
mortal blade
if you can host a website you can host the file yourself
mortal blade
host the file on the website
desert ember
When links expire To access the attachment CDN link after the link expires, your app will need to fetch a new CDN URL. The API will automatically return valid, non-expired URLs when you access resources that contain an attachment CDN URL, like when retrieving a message.
your bot just needs to fetch the message with the attachment, then update the link in the db
https://www.reddit.com/r/DataHoarder/comments/16zs1gt/cdndiscordapp_links_will_expire_breaking/
but also
If your app requires access the content from an attachment CDN link, you should fetch the contents from the valid CDN link and upload them to a secure, independent host that your app maintains access to.
await channel.fetch(id)?
yeah makes sense
but if you have a website, and you have a db... you can just store the images on the server.
how many images would you be storing?
spring bloom
Unless we're talking like 10+ gigabytes I doubt you'll run into any limit
shadow cape
It should be noted that discord is changing the expiry to 24 hours, which isn't much harder in terms of fetching new urls but slightly more of an inconvenience
But really, you're way better off hosting on-site or one of the many free sites like imgur and catbox (both of which have account systems to keep all your stuff in one place)
desert ember
please don't store large files in github
shadow cape
i mean, genuinely, is there a reason you're so insistent on storing them on discord?