That's adding that no other goalie better than Jarry is available. Big assumption.
Fair, but Jarry will also have just turned 26 years old with a 2nd round pedigree that'd be fully developed and he's already shown he belongs in the NHL well ahead of the expansion draft. It's quite possible if not likely that there'll be another goalie available that'll have a higher upside, but Jarry would be a young goalie ready to step into a starting role, which would make him an ideal target for an expansion team. A lot can change between now and summer 2021, panicking about who we're going to lose 18+ months from now isn't high up on my priorities list, but Jarry looks like a future starter in this league and I doubt there'll be an abundance of goalies that will check all of the boxes that Jarry does for an expansion team.
FWIW the cost thing is the only reason I'd even consider moving Murray, and he'd need to be steadfast on demanding a stupid contract for me to give it serious thought. Jarry is only a year younger than Murray, which completely undercuts the biggest reason Murray was chosen over Fleury the last time around. Say what you will about Fleury and/or Murray, but the age gap there was a decade. No GM in hockey was going to choose a soon to be 33 year-old goalie making nearly $5.75million against the cap coming off a 3+ GAA season over a guy who had significantly better stats on the same team, had just turned 23, and had won the Stanley Cup in each of his first two professional seasons. Even if time managed/manages to prove the decision wrong, it was still the obvious decision.
It is also worth noting that the Pens had Murray looking at 5 years of restricted free agency looming, while Jarry would be looking at just 2 come 2021. Even if Jarry progresses as well as anyone could hope, his status as affordable would be comparably brief. Unlike last time, however, there won't be a glut of high-end goaltending prospects all around the same age again providing an extra layer of security. When Fleury was dealt, Murray was merely the third highest drafted young goalie in the system. Jarry was the team's top pick in 2013 and Filip Gustavsson the same in 2016. Ultimately this means little this far out, but it is an argument for choosing the known quantity when Jarry barely counts as being younger.