Has it ever been explained (barring John Peel's book, The War of the Daleks which hasn't been widely accepted) how Skaro can exist when the 7th Doctor caused its destruction?
Given that Skaro's sun must be considerably smaller than a supergiant (otherwise Skaro itself could not exist) the explosion caused by the Hand Of Omega could well have been considerably weaker than a natural supernova. It's possible the planet itself survived, even if all Daleks on it were destroyed. It is worth noting that Skaro itself is seen in 'Asylum Of The Daleks', looking in a much worse state than in 'The Magician's Apprentice'. Possibly the Daleks restored their world to it's former glory in between those stories.
Having read up on this, first the Omega Device was meant to make a star go supernovae and become a black hole, and I think even a "small supernovae" would be quite destructive.
According to this reference: "At the time of broadcast, it unambiguously showed the onscreen destruction of the Dalek homeworld, Skaro", with the added comment that this was forgotten(!) when the series came back (in fact, even in the Dr Who movie since this involved the Master apparently being exterminated by the Daleks on Skaro).
However, tardis wikia also states here: "Skaro was apparently destroyed when, as planned by the Seventh Doctor, the Hand of Omega caused its sun to go supernova. The stellar explosion released a shockwave which quickly struck the nearby world. It ripped and burned the planet to smithereens. (TV: Remembrance of the Daleks) However, at least part of the planet persisted, though in ruins and with the conditions of its environment even worse than after the Thousand Year War. (TV: Asylum of the Daleks)".
I remember at the time there being some discussion about the Doctor destroying Skaro, since not only would he destroy the Daleks but also all other sentient life that also existed at the time.