What if, instead of a boring hum-drum "page not found" you had a little fun with the page?
If you're changing things on your website it's only fair to your visitors to let them know that a particular link is no longer working. But there's no reason not to have fun with the page and make it a less annoying experience for your visitor. This is actually another opportunity to insert your company personality. Consider a fun and interactive page or a pleasantly designed one that follows your marketing and brand standards. Take the opportunity to let your company shine.
The folks at Creative Bloq have put together a list of outstanding 404 error pages that visitors aren't necessarily disappointed to land on.