Perhaps a clever CSS rule would work?
Such as this one:
https://www.broken-links.com/2010/06/14/using-svg-in-backgrounds-with-png-fallback/
EDIT: Maybe this one is better:
https://www.reddit.com/r/css/comments/1ycbgi/fallback_background_image_when_first_is_not_found/
EDIT 2: Nevermind that one uses Angular. I'm certain though CSS is your answer...
Also, on the topic of SDK, Karol has a free one he made here:
Design Studio SDK: Fallback Picture Component
While it sounds like you don't want to use any SDK components, free or paid, maybe this helps others who don't rule out of SDK components.