The Viking probes ran out of juice. In fact the Viking 1 lander was
expected to keep running until 1994, but an unfortunate command
put the lander in Failsafe mode in 1982 and was not heard from again.

The Voyagers are still returning data to Earth and are expected to do
so until 2025, when their RTGs can no longer power even one of the
onboard systems.

Pioneer 10 and 11 lasted way past their warranties: Pioneer 11,
launched in 1973, kept signalling Earth until 1995. Pioneer 10 made it
all the way to 2002 and might even still be working, we just can't
detect its very faint signal any more.

An even earlier Pioneer, number 6, designed to monitor the Sun, was
still transmitting when they checked on it in 2000. Anyone know if it is
still being tracked?

There was a rumor I once read about a US Navy satellite launched in
1964 that was transmitting well into the 1990s, but I do not recall any
more information at the moment.

Some day we are going to need space probes that will have to last a lot
longer than 50 years when we start exploring other star systems.