It will, yes. We are aware of the change and in discussion internally with what we need to do in the future. Our current understanding though is that OpenGL is not being actively removed, rather it is deprecated, and so we are hopeful that things won't break for a while since we use fairly simple OGL functionality in current versions of Terragen. We will continue to test on newer versions of OS X and will do our best to keep the Mac version working smoothly, but it's definitely a frustrating thing to have to deal with.
- Oshyan