So will there be a time/window, to claim and that is it?
Is it going to be a 1:x ratio, and what's going to happen to the coins unclaimed?
There will be a time/window, it'll be announced later, watch this thread.
Unclaimed coins are impossible by design: all 98% to be claimed will be distributed in proportion to the balance of linked bitcoin addresses.
The math is very simple. If the balance of all your linked bitcoin addresses is 100 BTC, and the total balance of all linked bitcoin addresses of all users is 1,000,000 BTC, then this is the number of bytes that will be yours:
100 / 1000000 * 0.98 * 10
15 = 98,000,000,000