According to the article, the Phoenix has a reversible hydrogen fuel cell on board. Just a guess, but maybe it's filled with helium on the ground (for safety purposes),then generates hydrogen (from electricity and water) once aloft to replace any lost helium?
About #2 - I think the 'new' part they're touting here is no longer needing to ensure the telescope knows exactly where north and the horizon are. In other words, given a known location from GPS and some images of stars from the builtin camera, it'd be possible to calculate in which direction (az/el) the telescope was pointing. Is there a general term to describe this sort of thing?
Satellite is launched, goes silent after a few years due to electrical problems. Decades later, the onboard batteries have deteriorated such that they're just a short (no storage capacity), and the satellite works intermittently when the solar panels are exposed to enough sunlight.