Right now I would settle for the option to license it for commercial use again. SAS/C is crucially important for the AmigaOS 2.x/3.x platform because it is the best-integrated 'C' development environment for it.
Bingo. Asking for "open source" first might already scare decision makers within SAS/C, so I wouldn't go this route right now and would not set the priority on the license conditions too high.
The important part is not "open source or not", the important part is to get contacts to the decision makers within SAS/C, and *then* discuss potential options.
In the best possible case, they might be able to put a "price tag" on the source. Even getting it licensed again - as in "binaries for money" - would be tremendously helpful.