All soap characters 'disappear' from time to time. The actors sign anual contracts committing them to a set number of episodes, wwhich allow the writers flexibility in storylines, and prevents any character from becomg over-exposed Carla and Rosie should be exempt from this rule of course!)
The actors are allowed to work outside their soap, subject to certain conditions - no advertising, restriction on other tv work, and so on. They are also contracted regarding their appearence - no drastic change of hair style or colour, no gaining or loss of facial hair, tattoos, and similar. Years ago, overt suntans were banned, but this seems to have relaxed now, you see the occasional returnee looking decidedly 'healthy'.