My duck has been laying eggs, but is not sitting on them...How long will they last?

I have a wild mallard duck, a mallard drake and a call duck who I suspect is of dodgy parentage....she was sold to me as a brown call duck, but I suspect has a mallard dad, as she prefers to hang out with the wild ducks instead of the domestic ducks. I also have 6 hens and 2 aylesburys, and a white call duck. I have removed the eggs from the hens and domestic ducks but when blue eggs appeared, I left them as I assumed they came from my wild ducks, and were probably fertilised, and am eagerly awaiting ducklings. However the clutch has now got to 16 and nobody seems keen to sit on them. The night before last, the wild duck disappeared, tonight the drake did too. I have split the eggs into 3 piles, hoping maybe a hen will get broody and incubate them, as even if my wild duck returns, I dont think she can cope with 16. Has anyone any advise as to what to do next, and how long will these eggs have potential ducklings in them? Should I remove them and buy a heat lamp or an incubator for them?