See, I'm not so sure about the 'prepared' part, provided they have some factory support; look at MarcVDS, they have essentially dominated Moto2 championships even had the same rider from one category to the next, but their GP Team was an utter failure and ran out of funds i an embarrassing manner. That's not to say riders like Jack Miller didn't benefit from getting a ride, but look what it did to Lüthi (I just think they're a spec racing outfit); by contrast, look at what the Petronas Team have achieved in just their first year with some factory support (first with Franco and then Fabio once he cemented his role) and a star rider like Fabio to make it all come together--it must be hard for Jarvis to see how often Fabio outscored the works Team week after week.
I think its more along the lines of how close are Yamaha to winning a championship without him in 2021, and is it worth extending support to yet another satellite Team. If I'm honest, I think if he did the Sky46 thing and some how still decides to ride for it himself, it would be a pairing with Ducati not Yamaha. The amount of outpouring that would mean in sponsorship, merchandise money and Media exposure (Sky Italia is probably as big as Movistar+ was) would probably far outweigh anything Yamaha could bring to the table--which is probably sure to be a Mav/JLO spec bike like in '17, which Rossi has made it clear he doesn't do well on. Also, I'm guessing the big wigs at Iwata are tired of hearing the endless bitching, from both riders to be honest, that they'd probably just want to move on with their new stars.
It'll be odd to not see those massive plumes of yellow at Mugello or San Marino anymore, but seeing him in the back is probably not the way most of you want to see him either, so...