From today’s Open Europe news summary:
ECB to halt production of €500 note, but it will retain its value
The European Central Bank announced yesterday that it would stop printing the €500 note from the end of 2018 due to, “concerns that this banknote could facilitate illicit activities.” However, the bank confirmed that the note will always remain legal tender and will therefore continue to retain its value.
Source: ECB Press Release
Once cash has been eliminated, the ECB can implement its negative interest rate program on a large scale. In fact it probably doesn’t have to eliminate small bills, since it may be impractical and/or impossible for anyone to hold and use cash denominated in small bills for anything other than petty purchases.