Igig,
During training you will receive basic salary, which will depend on aircraft category and position. Not sure if Riyadh base is forced on new hires.
Attrition rate during training is mostly due to people failing or leaving due to various reasons, housing (or lack of it) being number one..... Saudia on 99,99 %of cases renew the contract, I cannot remember any case where they do not renew the contract after the 3 years.