The forward core hasn't been fit the last two years. Geno played Montreal like he needed elbow surgery after (he did) and NYI on one leg. Sid played Montreal and NYI like he was recovering from a core injury (he was). Guentzel, same with the shoulder surgery. Despite that Sid and his line still showed vs Montreal, Geno and his line vs NYI. If we want to go back four years, they had Geno, Kessel, and Brassard as walking wounded going into the Caps. The 2019 Islanders series is the only one where fitness hasn't been a major issue, and that iteration of the team sucked.
This is the fittest they've looked since the season where things got shut down.
Also, as pointed out before, this team has never liked facing well-structured defensive teams, regardless of team make up or star form.
So yeah, I think it's reasonable to think there might be a different result despite running back largely similar lines (most of which haven't been run back consistently through the periods). And the point that teams often break through after trying largely the same lineup for a while isn't without merit.
I'd also add there's nothing new or unexpected about stars having quiet series in successful playoff runs. Stamkos had 1 ES point vs NYI last year. If Stamkos wasn't playing in front of a goalie playing with a .940 shooting percentage, maybe that ends up being something that sends them home. Geno had one ES point vs San Jose in '16, Guentzel one ES point vs Ottawa in '17. Maybe if we'd have strong goaltending vs Montreal and NYI, we'd have got through and the stars would have got back in form and we're talking a different story (we'd have almost certainly got through). If we'd had even average goaltending in those runs, we'd have one cup max.
I'd be happier if they'd mixed up a few things in the top six and looked less wedded to GCR. But it'd not an unreasonable idea that the personnel in this configuration can do it.
You wont. No cap then so Zohorna, DOC, Angello will all be available. Possible others depending on the situation. They have no cap to call up guys right now.
Doubt Sully is going to change which players he relies on after a full season.
Also, maybe Zohorna aside, I'm not sure why he should. Angello isn't definitely better than Simon and Boyle and hot start aside, neither is DOC. It'd take a bit of optimism to say they're definitely equal.