I don't know who this Insigne guy is, but i don't think Pandev or Vargas are good enough to replace Lavezzi, especially the former.
I haven't seen Insigne, so I can't comment on him. The way Trequartista keeps banging on about him, though, I assume he's not useless.
Vargas hasn't shown anything since joining Napoli.
Pandev was very good last season - probably the best he had been since leaving Lazio. He's not going to move around and stretch defences the way Lavezzi did, but Pandev can link the play and is far more likely to produce an incisive pass than Lavezzi was.
Anyway, I was saying that Lavezzi will be missed by Napoli - but that the better squad depth could make them a stronger side over the course of the season so long as the players mentioned can even 70% replace Lavezzi between the three of them.