It's just knowing how NFC chips work.
In general, consumer standard NFC chips, which are the chips Nintendo puts in their Amiibos, have a lifespan of 10,000-15,000 reads/writes; YMMV. Industry standard NFC chips have 100,000 read/writes. Chips with a longer lifespan are very expensive, and I doubt Nintendo included ~$40 USD NFC chips in their ~$13 USD Amiibo products.
Your NFC Reader will undoubtedly die before your NFC chips do.
Here is a link to a typically used, Chinese-made, consumer standard NFC chip. It's easily assumed these (or something similar to these) are the chips Nintendo uses for their Amiibos. They have a read/write cycle of 10,000 and will store data for 10 years.