I think a draft is inevitable.
There's no way we don't get sucked in when Israel eventually bombs Iran or vice/versa and/or something goes "boom" in America and we have to blame Iran for it because if we blamed Afghans or Iraqis we'd have to admit we failed and we can't blame the Saudis if we want to continue to be able to drive cars.
A draft is also a great way for politicians to artificially deflate unemployment numbers.
Plus we were able to have an all volunteer army back when we never invaded anything bigger than New Jersey, so people would sign up figuring it would pay for college.
Now that you actually get shot at regularly when you sign up, people are signing up less.