During the bombardment of canterlot, was it normal missiles or balefire bombs? could true alicorns withstand a balefire bomb?

5821284
Canterlot was bombarded with regular missiles to get the Princesses to raise the shields. Then the pink cloud was released inside.

5821594

cool, so do you think a true alicorn with shields up, could withstand a balefire bomb, just one.?

5821599
Not likely. If the Black Book which is indestructible could be destroyed by one then it would likely have killed a true alicorn.

5821785
The crater alicorn was killed by balefire (Specifically, balefire eggs). Megaspell radiation might heal them, but they still have to survive the powerful shockwave and necromantic fire to get there.
5821962
To be fair, we don't know if the megaspells could destroy the Black Book. It was theorized that it might (And if it could survive a megaspell, it was still buried under a huge amount of rock and concrete, so "good enough" for the time being.

It's not entirely clear. There was a hard cut (Mostly because Littlepip passed out). Xenith said it was incredibly loud, which suggests to me that it didn't contain the spell. Then again, even if it didn't contain the spell, it wouldn't be clear if that was because it broke through the shield or because it just killed the alicorn.

Closest we get for sure is knowing that a balefire egg can kill a non-super-charged alicorn through her shield.