Virgin MK2 will almost certainly pull out of marginal and loss making routes, some of which which REX may be able to turn a profit on with a smaller aircraft and lower cost base. Regional jets might be a better starting point as they could replace the SAAB on longer sectors, and a lot of travel to and from regional airports is non discretionary. Trying to fill an airliner with highly price conscious bogans and make money while competing with two larger established operators doesn't always work, just ask Impulse and Tiger Airways.
Kendall Airlines had its fair share of problems when transitioning to RJs and CASA would certainly be keeping a careful eye on them.