If these things are going to arrive in Feb next year, then it is a reasonable bet that they are going to cobham, at least in the first instance.
Getting the aoc, whichever one it is, amended to support the 717 is not a quick thing, particularly if you need to build a check and training system from scratch.
Regardless if eastern/QantasLink has an ex Jetstar guy as HOFO, he is only one man and he doesn't wholly embody the experience required in order to successfully establish a check and training system for a new type, let alone transitioning a turboprop operation into a jet one. He may well be the seed from which this experience grows, but he cannot possibly do it all himself, there just isn't that many hours in the day.
Alternatively they might go to mainline, but again they would need to divert resources from the 737 fleet in order to do so. If that project isn't already under way then it is probably too late. The rumour mill is too good to have allowed that to get underway without someone letting something slip I would have thought.
None of this doesn't mean that cobham will keep the operation forever, just that I suspect it is unlikely that in the short term another operator will pick up a couple of stray airframes