I'm very sorry to hear of the loss of your furry friend.
Losing a pet is very hard any time it happens, but it makes it even more difficult when you suspect the cause may have been contributed to by the food you were feeding. The sad fact is, there is very little oversight with the pet food industry. They are allowed to put ingredients into their products which would never be allowed near a human plate. They are also for the most part self-regulating. Sure, the FDA announces recalls and approves/disapproves ingredients that can be used, but the urgency isn't there like it is when there is a situation with human products. Ultimately, some products inevitably get overlooked. That is completely understandable as humans should be prioritized. However, there needs to be a better system put in place. They also need to look into banning some ingredients which have proven over time to be linked to serious health problems, like for example ethoxyquin (a preservative banned in human food), propylene glycol (a key component of antifreeze), and menadione (a form of vitamin K which is banned for human consumption and considered a toxin) just to name a few.
I'm not sure if you have any other dogs and are now looking for a new food. If you are, I can highly recommend to you Nature's Variety Instinct, Nature's Variety Instinct Raw Boost, Merrick Grain Free, and Blue Buffalo Wilderness. We rotate these for our dog, along with canned products from those manufacturers and raw food from Nature's Variety. You can find all of these brands at Petco, and the Wilderness is also available at Petsmart if you have those stores in your area. I won't lie, they are pricier than Beneful. But, if you can afford them, they are very worth it, in my opinion.