Mark Beretta wouldn’t be an adequate male co-presenter on Sunrise once David Koch retires? Beretts has been presenting Sport for over 15 years and is hardly foreign to Sunrise viewers, I’m sure most would be fine if he were to become a main co-presenter when Kochie retires.
As for what should happen if/when Sam Armytage decides to leave Sunrise, I’m sure most here would agree that it really should be the presenter who was robbed in 2013! 
Realistically this won’t happen (especially in Perth where there’d probably be riots if Seven were to demote let alone sack one of Rick or Sue), but I personally think the idea of dual presenters in the smaller metro markets should be ditched on both weeknights and weekends if Seven are serious about cutting back costs. The ratings in Adelaide seem to suggest that viewers are remaining loyal to Seven News even with just one newsreader on weeknights.
They could probably get away with this in Adelaide & Perth, but the three largest markets probably still need weekend weather presenters for as long as Nine have them.
Really, I’m just imagining the “you need a forecast you can rely on every night of the week” type promos from Nine News (even if such spots would be pretty laughable in Sydney given the “barely any better than Tim Bailey” calibre of TCN’s forecasters) right now!