Their possession stats are quite strong (6th for CF%) and their goal differential is great (1st in the league), so the underlying stats for their play indicate it's not just them getting a bit lucky.
Is the play of individual players sustainable? Rinne is having a fantastic year, but he's considered a top 5 goalie anyways, so it's not like he's expected to regress much. Weber, Josi, Jones, Smith, Neal, etc are all playing at expected levels IMO, so shouldn't be regressing.
Forsberg, Ribeiro, and Wilson are the question marks. They're all having better than expected years, so any regression there could hurt the team pretty hard. That's where I'd place the question marks on sustainability for this team. I'd like to see them do well though, I like the idea of Weber staying with a small-market team and finding success there. If Weber were on a perennial contender like Chicago, I think he would have won 2-3 Norris' by now.