Expat contracts are fixed term and provide additional benefits compared to local terms, such as housing and school fees. If the contracted period is coming to an end the company decides not to renew they are perfectly within their rights, as would the pilot be if he got a better offer somewhere else.
Expats are a means of coping with changing requirements, easy come, easy go and paid above the odds to take this into account. Pilots in India are finding the same thing.
SIA offer local terms with less benefits but greater security. The expensive expats will be the first to go in any downturn, once things pick up again more expats will be employed with better conditions than the locals.
If you want a secure job with SIA, take local terms.