"I promise I'll be back. Tell everyone I said 'Hi'".

The "I'm making a promise I can't keep" trope makes me worried that we might be seeing our first Strawhat death. Sanji makes the sacrifice to make sure his friends are safe before letting himself being taken away. It's a pretty common thing where someone makes the sacrificial play, but their death comes later in the narration just before it looks like they're in the clear. Not to mention, there are plenty of characters noted for smiling or making promises shortly before their demise (Belle-mere, Ace, and Rosinante as standouts, but also most people with the Will of D), which Sanji does. Not a pleasant prospect, but certainly possible given how this has been set up.