You have two separare issues here
If you fail the drug test? That would be a basis for the military to separate you administratively.
The second issue is failure to show up to drill. That is a separate basis for administrative separation
So to answer your question, what if you do not go to drill AND you fail your test? Since either one, on their own, can be grounds for administrative separation, you can bet that the two combined would be grounds to separate. I would expect them to process you for separation...and they may attempt to give you an OTH discharge
Before they can award an OTH, they have to give you the opportunity to have a hearing...they would typically mail you this notification. If you do not respond to the notice, you waive your rights to a hearing. If you demand a hearing, they will give you a hearing, in front of a board of officers
who will decide if you should be separated from the military and if so, what the characterization of service should be