How to properly link to a client's constantly changing product

Site URL: https://www.%20anybodysautos.squarespace.com

My website is going to showcase a gallery of featured vehicles from local car dealerships. What happens if the dealer sells that vehicle and takes down their product page? I'm betting that they don't actually delete those pages, but I can't count on them having their own redirect.

Is there some kind of code that I can use on my website to avoid a 404 error when my link is about to take a viewer to my client's deleted page?

Ideally, a viewer would click on a gallery image on my website, and if it's about to go to a deleted page on the dealer's website, the code would bypass a 404 error and take them to the dealership homepage.

Thanks for any suggestions!

p.s. You need a password if you visit my site: AutoSales

You can't control this on your site.

You need to do this on the dealer's website.