unpublishing a former default variant results in 404

Hi, me again....what can i say

I have a product and it has some variants, and the default variant is out of stock not coming back.
So when i et another variant as deafault that works.
If i unpublish the former default variant, it results in a 404 of the whole product page.

I tried doing mass actions canonical urls but that does nothing.

How do i solve this? i dare not delete the variant as then i could not solve the 404 issue.
Thanks