You may have done some kind of operation that failed and caused the object involved to be lost. This happens most often when people try to boolean objects that do not follow the boolean rules..

chances are if they are gone, they are just gone and you will have to go back to the latest incremental and start over from there. I do not know what version of maya you are using but maya 2012 is buggy as hell. Of course autodesk absolutely flat out denies this and will blame it on your hardware, the day of the week, the phase of the moon, the size of your underwear, and will not take responsibility for the crap that is maya 2012!

But they will waste a shit ton of man power creating new versions of tools that already work like the split polygon tool! Of course they will rush to create the SAP version to get people to pay more money so they can have the 2012.5 version that is just as broken as 2012, and I am sure they are racing to maya 2013 as I write this with lots of trivial features while ignoring all the bugs they are creating!

GG Autodesk!