I also think a trainee that leaves, whether hardship or ERR, leaves as a training failure. There were two that were thinking about leaving and I told them to look into it because they would be much better off getting certified first.
If you look at the training success rates spreadsheet in the resources section on this site, you'll see what is used to calculate the training time in years and training success rate columns on the PPT. At my last facility we didn't have any trainees wash/terminated via TRB. But we had three trainee resignations (two for performance and one went back to contract tower), one trainee hardship and one trainee transfer (both transfers pre-ncept). And all five have been counted as failures on the training success rates spreadsheet and so on the PPT it shows us as having a 76.9% training success rate. It threw a lot of people off when the first saw it because we haven't had anyone wash but still showed a 76.9% success rate on the PPT.
So if you have a trainee leave for whatever reason, expect it to affect your trainee success rate on the PPT once that fiscal year is included in the training information on the PPT.