Due to over-tourism, they removed from the center, but a colleague from NET told me they will put it back somewhere else.
Is this true? If so, does anyone know when and where?
It seems they will come back, but when and where is still unknown. From local news site AT5 (December 3rd):
Ze worden opgeknapt en daarna zullen ze rondreizen door de stad. Welke plekken ze zullen aandoen, is nog niet bekend.
They will be restored and then they will travel around the city. The places they will visit are not yet known.
The Parool newspaper reports other places where you can still visit similar letters (there are 5 sets in total): Presumably you can still see them at Schiphol Airport, at the Hoekenrodeplein (haven't found this one yet) and near the Sloterplas.
According to the I Amsterdam characters page of the I Amsterdam website, the characters are traveling around: