The risks of continuing to use an End of Life device are generally one or all of these:
You can no longer get a replacement device via Meraki Support, if the hardware fails.
You will no longer receive firmware updates or fixes, lincluding for bugs and/or security fixes.
Meraki Support will no longer provide substantial support in the event that you have a problem with the device.
Remember too that, in order to keep the device working, you do still need to ensure the license is kept up. So; the relative value received from that license drops significantly. In most cases, any residual value for remaining license time on a device you want to replace will (or can) be retained for a new Meraki device, deployed in its place.