Back in 2008 intel announced that they would extend the life cycle of the socket 775 chips until 2011. According to this site: Intel® Core
all but a couple of Core 2 Duo chips are still in production - but who knows how current that intel webpage is?
As long as intel is producing new socket 775 processors then motherboard manufacturers will continue making socket 775 motherboards and RAM manufactures will keep making RAM for them. IMHO, Intel will stop producing the chips when sales drop below some number that only Intel execs know. When all the socket 775 chips reach end-of-life then motherboard manufacturers will stop producing motherboards and they will become available only as long as inventories last.
Most times they terminate processor lines on a schedule. But the 775 has been such a rock solid performer that I think they are going to ride that horse until it collapses to the ground.