Hi chris, well the nearest cemetery to Abergwynfi would be Cymmer, so perhaps that would be the best bet to find if he was buried there.
And in answer to your 2nd question, no I do not have a death certificate for his wife (mary ann thomas), its such a common name and too many records come up for the BMDs, so without a narrower date it'd be a lot of money. As with a marriage certificate, i have as of yet, not ordered one, so another route to follow there to help with the dating.
And the only other piece of information i could give you, is that he had 11 children and the story is that he could not afford to look after them or something along those lines, im not too sure how he did it though.
Regards, Josh.