Booked BOS=>JFK=>SIN in biz, through SQ, ticketed by SQ.

A friend booked this exact itinerary a month ago and the BOS=>JFK flight (on Jetblue) was delayed and she missed the connection. The flights are very full these days so she had to wait 2 days to fly and she had to move back to economy.

Our flight is coming up and weather is looking bad, and with all the operational issues Jetblue and others have had, we called SQ to suggest we move the BOS=>JFK flight earlier.

Agent: "Great, I can do that. It will cost $6000"
Us: "Really? What happens if we miss the flight?"
Agent: "There will be a no show charge"
Us: "Really?"
Agent: "Yes"
Us: "Does that make sense?"
...

The JFK=>SIN flight in biz appears full for next couple days. We very much do not want to miss our connection.

Has anyone successfully proactively de-risked a situation like this?

• It appears we can do a same day change on Jetblue for $75 per person but we are afraid the res gets unlinked and our bags won't be checked through.
• We can drive to JFK, but if we don't show for the Jetblue flight we are afraid we will lose our booking on the SQ flight. And if we call to change that, it will trigger another $6000.

Any advice appreciated. Thanks.