Okay, then there maybe is good news here:
Currently, archiving accounts is “only a feature request” (Archive old accounts), but there are some signs, an archiving function is going to come in the near future - see e.g. this post and link there: Archive old accounts - #162 by Nail1684
But, no one of us knows at the moment, when it will be released.
If you are not in an absolute hurry, I personally probably would wait (the next one or two release cycles / months)…
Please write back, if you can’t wait 
- to explore other options.