So what happens if I change operating systems in a few years?
There are separate downloads links for Window and mac.
I found this, but it doesn't get into the different OS question. Should I also be downloading separate OS content for a potential OS change?
The expiry only relates the the main Sounds Libraries for a product.
The download period is 180 days for each product Sounds Library, from the date of product Registration.
There is a reminder on the download page and in the Product Manager ("IKPM") to keep a back-up copy of the downloaded files so that they do not need to be downloaded again.
You can reactivate ALL of your sounds downloads access by purchasing 1 (one) 'Download Reactivation Credit' in IK Multimedia's webstore.
The price is 9.99 (excluding VAT)
Reactivation will open download access for a further 180 days for all registered products.