In my opinion, a well played necro is a very hard fight for the shaman, mainly because the necro isn't going to put himself, or easily be put, in a situation that is easy for the shaman. He can match your summon tricks, an army complicates things 10x etc. On the other hand, I've also can't remember ever being scared of a necro with my shamans. The only necro death I ever had across three shamans was to post-lich Drekvah as Ezgrint, and he only got me once. Plus, shaman vs lich is HANDS DOWN the worst match up in the game, at all, by a large margin.

If a necro has you slept, sure, you're not in an ideal situation but you should survive pretty easily. Unless sanc + fly + protective shield all drop before the sleep wears off I'm betting you're surviving. Even if everything drops, you're still not dead to rights. Set a really high wimpy, quaff that teleport potion. Cure your shit.

Note: Once a necro gets forget I'm way more cautious about fighting them. Sleep + forget is an easy shaman killer.