https://www.motorsport.com/f1/news/why- ... 9-1045886/
This article makes some pretty good points:
"This will also allow McLaren to keep Alonso on its books in the hope of bringing him back to F1 when its car is good enough to win. Alonso would be able to keep tabs on the team, certainly test the 2019 car and perhaps even turn up in some races to keep his hand in and monitor progress."
An IndyCar deal would also allow Alonso to see out the World Endurance Championship superseason with Toyota. The Sebring 12 Hours and Le Mans certainly won't clash as those weekends are left clear for IndyCar drivers, while the Spa round takes place on the first weekend of May, which will surely be a blank given that three weeks of action at Indianapolis follow.
That would give Alonso a second crack at ticking Le Mans off the bucket list should he not win it this weekend. And even if he won it, it could also allow him to take the World Endurance crown. He could end June next year a two-time Le Mans winner and the Indy 500 champion.
Given McLaren's focus will increasingly turn to 2021, when F1's rules are reset, perhaps he could even have a two-year run at Indy500
"Because you didn't come here to make the choice, you've already made it. You're here to try to understand why you made it. I thought you'd have figured that out by now." The Oracle, Matrix Reloaded