Well, it isn't quite that bad but he certainly has a higher threshold than most to get back to the 40 man.
His salary of 25.5 + 1M buyout is a sunk cost at this point (unless he shows enough that some team is willing to take part of the contract on).
The extra cost is the 17.5% luxury tax for this year on his AAV average of 6.2 = roughly 1.0M (some of his salary has already counted toward the LT threshold) for this year.
In 2016 and 2017, although his salary is much higher (9M and 11M), the AAV doesn't change. However, the penalty for being over the LT increases to 30% for the 2nd year (tax 1.86) in a row over and 40% (tax 2.48) for the 3rd. At this point, it does appear that the RS could certainly go under the LT threshold in both 2016 and 2017, with or without Craig on the 40 man roster and if that is the case there is no further savings. Obviously, it is 6.2 - .5 (min) easier if he is not on the roster.
In the end, if Craig tears up AAA for 2 months, I would think the RS would think it is worth bringing him up. Whatever money he cost in LT, he would have easily saved by increasing his value to another team. However, I think Craig will have to prove himself over a much longer time than what would have been the case if there were no LT implications. The greater likelihood if his success continues in AAA and the RS have a full contingent of OFers, is that the RS trade him getting another team to take a portion of Craig's salary while eating some. It just seems that this threshold (having some value to another team) would happen before he surpasses the RS threshold of taking the potential LT hit.