There are Operators in the Regiment who have been there since the first few SOBQ(now called SFC) courses. So no, after 3 years you won't be posted out. How ever, I would imagine the standards expected of its members would be high. You probably wouldn't last long in the unit if you fail a drug test, or are arrested for DUI, etc.
There is no officer SF Op trade, so it may be more difficult for them to make a career within the regiment due to career progression and career managers. However, just because they get posted out doesn't mean they can't return.