As already mentioned on this thread, you haven't provided many details which makes giving you advice difficult. That said, your situation sounds complicated and posting all of those details might not be a great idea either.
From this thread and your prior postings, it appears that you are a US MD, failed your surgery clerkship and Step 2 requiring a retake, had a medical LOA in medical school, applied but didn't match to psych, and appear to have SOAP'ed (or scrambled) into an FM spot. Then you developed a substance problem (or recurrence of a substance problem, if that's what your medical LOA in school was for) and was out on leave. Now you're just back, and missed a day of work.
As a PD, here's how I would look at this situation:
1. First of all, you don't get a "day off" if you have no clinic patients scheduled. You are paid to come to work, you come to work every day -- unless it's 100% clear that you have the day off (often because you are working the weekend).
2. If I have a resident who has a history of substance abuse, and they miss a workday, my first assumption is that they are using substances again. I would put you out on administrative leave effective immediately, and you would be tested, today, for substance use. Refuse the test and you're fired on the spot. Fail the test and it depends upon what's happened before. You would be out on leave until your test comes back clean.
3. Assuming you test clean, It would depend upon what else has happened before. If you have missed work days in the past, even if due to your substance problem, you might be terminated over this. If your attendance had been stellar to this point and you were able to convince me that this was a true mistake, you would be put on a remediation plan (or any current remediation plan updated) to include this, and make it clear that any further major professionalism violations will lead to termination.
I agree with the above comment. Your goal should be to be the best resident in the program. "Just getting by" is likely to result in a bad outcome.