Yodelin continued to operate after the 1971 avalanche. I skied there at least once in the 1972-73 season.
I believe that the avalance hit the residential development they had up there, not the ski facilities. Once the real estate deal was gone, though, there wasn't much point to the ski area (if there was much point to it in the first place, which is debatable). But they did limp along for awhile.
Note that Stevens bought Yodelin's equipment out of bankruptcy in 1976. This suggests that Yodelin was still around until not long before that -- perhaps 1975, or maybe 1974.