You can come up that north ridge from Abinuea Canyon, you just have to start somewhere down slope to avoid the dangerous spots.
I've come over from the trail to Agassiz, and up from Freidline prairie road and the south ridge to Agassiz. Take the route from the weatherford trail, as there is still a trail up there leading to the Agassiz summit. The south ridge is loose and brushy.
Agassiz was closed in 1984 to placate natives who didn't want Snowbowl expanded. There is not much veg up there, and with the rocky conditions, and exposure, there likely never was. Agassiz never should have been closed. The trail keeps 99.9% of the hikers in check and protects the very limited "endangered" senecio species that is endemic to the Peaks. Also, it tends to grow further down than the bulk of either trail, and does best on the western ridges just above treeline in places most people never visit, but elk and mule deer do, and they don't care what they step on. I've seen them, so they are there.
Hike Agassiz, dry or in snow. I have.