It would only be logical to see a successor device if that suited Altera's product road map. This part is only an Altera product as a result of their acquisition of Enpirion. It's not Altera's core business. So, I'm not surprised they're dropping the part.
There are plenty of devices, from far more popular power converter brands, to chose from - e.g.
ti's tps56121 (
http://www.ti.com/product/tps56121). Altera also have a strong partnership with Linear Tech - try their
ltm4627 (
http://www.linear.com/product/ltm4627) - who are frequently used on their development boards. Why compete?
As to why your devices are burning out - I can't make out your schematic. How much output capacitance do you have? Too much might cause this. Could you have a build fault? Can you power your load from a bench supply?
Cheers,
Alex