Here's a nice obit in The Los Angeles Times on Mr. Hart. It quotes him as saying, "The end of the world is approaching, maybe by the year 2010." If he's right, then he's only missing out on about three years.
And here's the Associated Press obituary, which says that both his strips will continue. According to the article, "Family members have been helping produce the strips for years, and they have an extensive computer archive of Hart's drawings to work with." If they said that about some strips, I'd be skeptical. But Hart often reused old drawings and just altered the lettering on them. So B.C. may not change much without him.
Lastly, this obit from the Gannett Service is the longest I've seen and it covers many of Hart's more admirable, unheralded deeds. If you only read one of the three, read this one.