All the fans on these boards are probably going to be replaceable by their RMA (Aorus has advanced RMA https://service.aorus.com/advanced_repair.php
for a minor fee if you're in the USA at least for Intel Z390) and if it isn't a proprietary fan then it will be able to be ordered from places such as Digikey ,Mouser, and Newark ; if it's proprietary somewhere from aliexpress or dhgate if not elsewhere in China. ASUS/MSI/Gigabyte/EVGA all obtain GPU cooler fans from Powerlogic (and Everflow) while I've seen the Asrock X570 Taichi uses Everflow as their OEM (FirstD for their GPUs).
I feel that there is going to be an aftermarket to replace them with a new generation of chipset heatsinks such as the Thermalright HR-05 anyhow. It's a bit early for any announcements but unless all future PCIE 4.0/PCIE 5.0 chipsets somehow lower power use by a large amount it will be inevitable : X570 chipset is already on 14nm and I don't think that it's economically feasible to start make 7nm chipsets in the near future until 7nm EUV is a mainstream matured process.