There are definitely a large number of SAS pilots in EK on leave of absence or leave without pay, whatever you want to call it. Also some ANZ pilots, I understand, and before it went titsup, Ansett unofficially parked a few people at EK, most of whom had every intention of returning to AN when the company called for them. There were also a few Brits here some years ago in a similar situation. I understand they'd come equipped with some pseudo acceptance of resignation letter from their company, but they made no secret of the real situation.
The recruiting situation today is far more critical for EK than it was only a few years ago, so my guess would be that anyone lucky enough to be in the situation of having right of return would be treated by EK a bit like the way the military used to treat homosexuals - "if you don't tell us, we won't ask you".