it is not dead, it is just sleeping

Phoenix Lander on Mars has ceased operation as winter moves in, power ran out and batteries died.

Phoenix Mars Lander has ceased communications after operating for more than five months. As anticipated, seasonal decline in sunshine at the robot's arctic landing site is not providing enough sunlight for the solar arrays to collect the power necessary to charge batteries that operate the lander's instruments.

Mission engineers last received a signal from the lander on Nov. 2. Phoenix, in addition to shorter daylight, has encountered a dustier sky, more clouds and colder temperatures as the northern Mars summer approaches autumn. The mission exceeded its planned operational life of three months to conduct and return science data.

See also Phoenix site at LPL

I don't think it will come back to life next martian summer. Unlikely the batteries will recharge and not much chance the electronics would come back on.

Be interesting to hear what the analysis of the samples shows in the long run.