As I understand the process, he (Aldon Smith) appealed the one year suspension and lost. His suspension then started on 11/17/15. On 11/17/16, his suspension was completed, but he still had to apply for reinstatement. The reinstatement process (conducted by the league) includes a full investigation into him completing all mandated requirements during his suspension (attend all rehab/meetings, meet and pass all urinalysis tests, and basically have no evidence of wrongdoing during that year). The league has 60 days from the time he applied for reinstatement to do their due diligence. That 60 days will be up on 16 January (I erroneously stated 14 Jan earlier). So, the league will have to issue a decision by then (they can issue the decision earlier if they so choose).
So, assuming that Gregory will get a one year suspension coming up here soon (by next week, if at all), we can expect that he will miss the entirety of next season and be reinstated early in the off season. We'll see him next in 2018, if at all. Hope I answered your question.
I missed addressing the last part of your post. My understanding is that he will be suspended at the conclusion of his current suspension (next week), but he will have the opportunity to appeal that. So yes, given that scenario, he would be able to practice and play until his appeal is heard and ruled on. He could possibly play through the playoffs unless they complete (and deny) the appeal before the playoffs are over. If I'm wrong about this, someone will come along with better info, I am sure.