Especially if the second attack is a necessary consequence of the first (e.g. the raiders were after something, and heroic protagonist(s) prevented them getting it the first time - in such a case, not having a second attack would require explaining).

Or if the first raid netted them such leet l00t that they considered the place easy pickings.

What happened historically? Were there Vikings where the target was a settlement known for its prosperity, a case where the raiders would hold back from pointless destruction on the grounds of making sure there'd be better pickings five years down the line? (As opposed to the extortion rackets that some of them ran, up to and including Danegeld.)