I think PNG and SVG inherently solve somewhat different problems in the realm of image representation, so there are going to be cases where each of them has the clear upper hand. However, with pixel density going up and file sizes and network bandwidth not being the limiting factors in many cases, I'd guess SVG will command increasingly bigger share of uses.
SVG has been out for awhile, long before Retina design became a part of the web development workflow, and yet, when faced with the challenge, most web shops didn't swap to an SVG workflow.
They just designed everything at twice the resolution.
Even Apple, who was leading the way for a hot second there on HDPI and vector assets, has swapped to mostly using 2x image assets.
The whole "will we swap to vectors?" debate already happened.