These are a current necessities, but nothing to sanctuarize for the future. The only thing that should remain stable in Europe are ideas, and the Swiss got it better on their notes
Although the ECB does not today "withdraw" notes in the sense that they cease to be valid for most purposes, it does deliberately destroy old notes and issue new ones with different images to replace them, so the original series must be getting pretty rare by now - not rare enough to be worth serious collectors paying money for it, but your ten year old may never have seen an actual old Euro €500 note even though in principle those still are valid money in the Eurozone.
Big part of the reason for this appears to be security. Many years ago a high-ranking official from Finnish central bank told in an interview that bank notes need to be redesigned approximately once per decade. Reason is that it takes about that long for the materials and printing technology to get commoditised enough for criminal enterprises to be able to start manufacturing "high-grade" forgeries at any real scale.
Every generation of bank notes employs a whole bunch of newly developed technologies and tricks that make the notes themselves distinctive, as well as incredibly difficult[ß] to forge.
ß: Some of it is down to tightly locked down and guarded speciality supply chains. Some is due to advances in microprinting and ilk. If you had unlimited resources, you could arrange to have the necessary equipment, supplies, staff and materials to print your own forged money. It'd just be slow, low-yield and very expensive.
The selection of people is also quite poor but that's because people are a poor choice: Most notable historical people are very linked to specific countries, often against other countries so picking neutral ones is hard. They also clearly decided to have an equal number of men and women, which makes it even harder. Obviously there aren't enough different banknotes to represent every country, either.
Faces are a terrible idea for a common currency shared by 21 countries.
You have to pick one writer, good that the English left for good so Shakespeare's out, but how do the French feel about Cervantes vs. Victor Hugo?
The Poles complaining that they didn't get enough recognition because Marie Curie's maiden name isn't given enough prominence should tell you all there is to know about this being a good idea.
I don't think anybody would mind since there's already Marie Curie, which is an obvious choice because she's both Polish and French. I don't know how the Polish take it but the French have no particular feelings about her being Polish as well.
But why are a Greek-American, and an - unknown to the majority of Europeans - Austrian in there?
How many counties more populous than Austria are unrepresented? Do all EU countries count, or just EZ? (Poland is not EZ, is represented, still complained)
It's an impossible list. Europeans don't necessarily have shared heroes, and if they did, some of these wouldn't be top 6.
As for the smaller countries- well let's face it do you think anyone in Europe gives a shit about Dutch or Estonian history and culture? Its France and Germany all the way down I'm afraid. At least we still have the veto.
And no one gives a shit about the (18 million) Dutch, but we picked Bertha von Suttner.
I'd like the birds front with the other option for the back (public squares or something?)