Ferrari's lead driver has squandered two chances of winning titles with self inflicted errors. Strategists make mistakes some times, like Mercedes guys did in Australia, Bahrain and Austria that costed them wins. So far, Ferrari made one reasonable mistake of sending out the drivers on Inters in Japan. Otherwise, they have done a pretty good job of managing the races. There were times when they made the right decision in the given context, but things didn't turn out to be how they wanted. It was Mercedes' leading driver that made amends for some of the strategy mistakes and brought home valuable haul of points, whereas Ferrari's leading driver has thrown away a great deal of points. Ultimately, that has turned out to be the biggest differentiating factor.
Can Ferrari afford a similar fate for a 3rd time next year? If the Mercedes and Ferrari start the next season on par, there is no reason to believe the story is going to be any different than this year's. This sounds very pessimistic, but there is no reason that generates optimism. In the current racing form, Vettel needs the car to be half a second faster than Mercedes to beat Hamilton in qualifying to start ahead and stay ahead, which he does the best and of course, without rain.
Regardless of how irrational it sounds, but bringing Alonso back might just save the blushes, at least on track racing issues might get sorted out. With Vettel and Alonso in the same team, Ferrari might just outsmart the Mercedes in Constructor's championship. Good to have at least a team championship. On sunny days, when both Ferraris are out ahead, Hamilton would most likely stand no chance of beating the Ferraris, when those Ferraris are being driven by two multiple world champions. If they can manage to do that more consistently, then one of their drivers might even end up winning a WDC for sure.
But I guess, I know Ferrari most likely wouldn't want to do that for many hypothetical reasons. If the interests of Scuderia is what matters, then this decision is definitely be a masterstroke. Leclerc can wait, in the interest of salvaging pride back to Scuderia.