One thing's for sure, if you use two smaller cards instead of one big one, you've just doubled the chances of having a problem. 32Gb is usually the most economical size in Gb per pound.
Total card failure is actually very rare. If you delete or erase images accidentally, or reformat a card by mistake, the images are still there intact. All that's happened is the card controller has been instructed to over-write the data cells, but if they haven't been, ie you stopped shooting as soon as you noticed a problem, all will be well. Free programmes like Recuva will get the images back in a few minutes.
Or the card controller can go down, meaning the images are there but can't be accessed. A specialist company can get those back. Even if some data cells have failed, it's very likely most or all of the images will be there, because all data is spread evenly over multiple cells.
The most likely cause of total card failure is physical damage, but even then you might be in luck - flash memory is very robust.