There's a simple rule I follow to solve that problem: If it goes in the sidebar (or a toolbar) it should be an SVG. It's the only way to ensure it will fit and scale no matter the screen size or device. With media queries you can even ensure that they get spaced properly (need more space between icons on smaller screens).
Pictures are they only problem that needs to be solved at this point.
Unless something's changed since the last time I looked, media queries are only screenwise so they don't gracefully handle having a block in a small sidebar versus a "central" content section. The sidebar images could actually grow from a big to a small screen (because content is linearised and the "sidebar image" now takes the whole width of a small display, rather than a small part of a big display)