If he was out for the season the blazers could file injury exception to replace him on the roster and that hasn't tooken place yet so until that's happens you can consider him coming back this year.
I don't know if a disabled player exception counts against the cap (and tax). If it does, that could explain why it hasn't been used. Another factor is that a DPE for Zach maxes out at 2.7M, so that's not really much more than a veteran minimum deal I don't think you can read any tea leaves about Zach from the DPE