? - Purdy had a complete tear of his UCL. Allen didn't. Both of his UCL injuries were sprains. If Allen had a complete UCL tear, he would have missed a season.
Also, playing with a torn ligament in a toe would make Allen a pretty immobile QB. That's not his game, and I would anticipate the Bills hoping for the best with Trubisky and getting Allen back fully healthy for the final 3-4 games and playoffs.