I have heard that the ping device should have stopped transmitting a long time ago.
It just passed its nominal 30-day battery life. But that's only its nominal battery life. Good engineers are conservative about such things, so, hopefully, it likely will last a while longer.
The president of the company that makes the pinger, Anish Patel, said it doesn't cut off suddenly but gradually fades out as its battery runs out.
However, he also said that Malaysian Airlines had not sent in any pingers for battery replacement since about 2010, which means that either the batteries are quite stale or Malaysian Airlines had found another source for battery replacement.
Sort of like the NASA space probes still operational many years beyond their life expectancy.